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For loop

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</style><table class="sidebar nomobile nowraplinks"><tbody><tr><th class="sidebar-title"><a href="Control_flow#Loops" title="Control flow">Loop constructs</a></th></tr><tr><td class="sidebar-content">

<ul><li><a href="Do_while_loop" title="Do while loop">Do while loop</a></li>

<li><a href="While_loop" title="While loop">While loop</a></li>

<li><a href="Foreach_loop" title="Foreach loop">Foreach loop</a></li>

<li><a href="Infinite_loop" title="Infinite loop">Infinite loop</a></li>

<li><a href="Control_flow" title="Control flow">Control flow</a></li></ul>

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In <a href="Computer_science" title="Computer science">computer science</a>, a for-loop or for loop is a <a href="Control_flow" title="Control flow">control flow</a> <a href="Statement_(computer_science)" title="Statement (computer science)">statement</a> for specifying <a href="Iteration" title="Iteration">iteration</a>. Specifically, a for-loop functions by running a section of code repeatedly until a certain condition has been satisfied.

For-loops have two parts: a header and a body. The header defines how the loop will iterate, and the body is the code executed once per iteration. The header often declares an explicit <a class="mw-selflink-fragment" href="#Loop_counters">loop counter</a> or loop <a href="Variable_(computer_science)" title="Variable (computer science)">variable</a>. This allows the body to know which iteration of the loop is being executed. (for example, whether this is the third or fourth iteration of the loop) For-loops are typically used when the number of iterations is known before entering the loop. A for-loop can be thought of as <a href="Syntactic_sugar" title="Syntactic sugar">syntactic sugar</a> for a <a href="While-loop" class="mw-redirect" title="While-loop">while-loop</a> which increments and tests a loop variable. For example, this JavaScript for-loop:<div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>for (let i = 0; i < 5; i++) {

console.log(i);

}

</pre></div>Is equivalent to this JavaScript while-loop:<div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>let i = 0;

while (i < 5) {

console.log(i);

i++;

}

</pre></div>Both will run <code>console.log()</code> on the numbers 0, 1, 2, 3, and 4 in that order.

Various keywords are used to indicate the usage of a for loop: descendants of <a href="ALGOL" title="ALGOL">ALGOL</a> use "<style data-mw-deduplicate="TemplateStyles:r886049734">

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</style>for", while descendants of <a href="Fortran" title="Fortran">Fortran</a> use "do". There are other possibilities, for example <a href="COBOL" title="COBOL">COBOL</a> which uses <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">PERFORM VARYING</code>.

The name for-loop comes from the word <a href="https://en.wiktionary.org/wiki/for" class="extiw external" title="wiktionary:for">for</a>. For is used as the <a href="Reserved_word" title="Reserved word">reserved word</a> (or keyword) in many programming languages to introduce a for-loop. The term in English dates to <a href="ALGOL_58" title="ALGOL 58">ALGOL 58</a> and was popularized in <a href="ALGOL_60" title="ALGOL 60">ALGOL 60</a>. It is the direct translation of the earlier German <a href="https://en.wiktionary.org/wiki/f%C3%BCr#German" class="extiw external" title="wikt:für">für</a> and was used in <a href="Superplan" title="Superplan">Superplan</a> (1949–1951) by <a href="Heinz_Rutishauser" title="Heinz Rutishauser">Heinz Rutishauser</a>. Rutishauser was involved in defining ALGOL 58 and ALGOL 60.<a href="#cite_note-1">[1]</a> The loop body is executed "for" the given values of the loop variable. This is more explicit in <a href="ALGOL" title="ALGOL">ALGOL</a> versions of the for statement where a list of possible values and increments can be specified.

In Fortran and <a href="PL/I" title="PL/I">PL/I</a>, the keyword DO is used for the same thing and it is named a do-loop; this is different from a <a href="Do_while_loop" title="Do while loop">do while loop</a>.

A for-loop statement is available in most <a href="Imperative_programming" title="Imperative programming">imperative programming</a> languages. Even ignoring minor differences in <a href="Syntax_(programming_languages)" title="Syntax (programming languages)">syntax</a>, there are many differences in how these statements work and the level of expressiveness they support. Generally, for-loops fall into one of four categories:

<div class="mw-heading mw-heading3"><h3 id="Traditional_for-loops">Traditional for-loops</h3></div>

The for-loop of languages like <a href="ALGOL" title="ALGOL">ALGOL</a>, <a href="Simula" title="Simula">Simula</a>, <a href="BASIC" title="BASIC">BASIC</a>, <a href="Pascal_(programming_language)" title="Pascal (programming language)">Pascal</a>, <a href="Modula" title="Modula">Modula</a>, <a href="Oberon_(programming_language)" title="Oberon (programming language)">Oberon</a>, <a href="Ada_(programming_language)" title="Ada (programming language)">Ada</a>, <a href="MATLAB" title="MATLAB">MATLAB</a>, <a href="OCaml" title="OCaml">OCaml</a>, <a href="F_Sharp_(programming_language)" title="F Sharp (programming language)">F#</a>, and so on, requires a <a href="Control_flow" title="Control flow">control variable</a> with start- and end-values, which looks something like this:

<div class="mw-highlight mw-highlight-lang-pascal mw-content-ltr" dir="ltr"><pre>for i = first to last do statement

(* or just *)

for i = first..last do statement

</pre></div>

Depending on the language, an explicit <a href="Assignment_(computer_science)" title="Assignment (computer science)">assignment</a> sign may be used in place of the <a href="Equal_sign" class="mw-redirect" title="Equal sign">equal sign</a> (and some languages require the word <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">int</code> even in the numerical case). An optional step-value (an increment or decrement ≠ 1) may also be included, although the exact syntaxes used for this differ a bit more between the languages. Some languages require a separate declaration of the control variable, some do not.

Another form was popularized by the <a href="C_(programming_language)" title="C (programming language)">C language</a>. It requires 3 parts: the <a href="Declaration_(computer_programming)" title="Declaration (computer programming)">initialization</a> (<a href="Loop_variant" title="Loop variant">loop variant</a>), the <a href="Boolean_algebra" title="Boolean algebra">condition</a>, and the advancement to the next iteration. All these three parts are optional. This type of "semicolon loops" came from <a href="B_(programming_language)" title="B (programming language)">B programming language</a> and it was originally invented by <a href="Stephen_C._Johnson" title="Stephen C. Johnson">Stephen Johnson</a>.<a href="#cite_note-ken-2">[2]</a>

In the initialization part, any variables needed are declared (and usually assigned values). If multiple variables are declared, they should all be the same type. The condition part checks a certain condition and exits the loop if false, even if the loop is never executed. If the condition is true, then the lines of code inside the loop are executed. The advancement to the next iteration part is performed exactly once every time the loop ends. The loop is then repeated if the condition evaluates to true.

Here is an example of the C-style traditional for-loop in <a href="Java_(programming_language)" title="Java (programming language)">Java</a>.

<div class="mw-highlight mw-highlight-lang-java mw-content-ltr" dir="ltr"><pre>// Prints the numbers from 0 to 99 (and not 100), each followed by a space.

for (int i=0; i<100; i++)

{

System.out.print(i);

}

System.out.println();

</pre></div>

These loops are also sometimes named numeric for-loops when contrasted with foreach loops (see below).

<div class="mw-heading mw-heading3"><h3 id="Iterator-based_for-loops">Iterator-based for-loops</h3></div>

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</style><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Foreach_loop" title="Foreach loop">Foreach loop</a></div>

This type of for-loop is a generalization of the numeric range type of for-loop, as it allows for the enumeration of sets of items other than number sequences. It is usually characterized by the use of an implicit or explicit <a href="Iterator" title="Iterator">iterator</a>, in which the loop variable takes on each of the values in a sequence or other data collection. A representative example in <a href="Python_(programming_language)" title="Python (programming language)">Python</a> is:

<div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>for an item in some_iterable_object:

do_something()

do_something_else()

</pre></div>

Where <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">some_iterable_object</code> is either a data collection that supports implicit iteration (like a list of employee's names), or may be an iterator itself. Some languages have this in addition to another for-loop syntax; notably, PHP has this type of loop under the name <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for each</code>, as well as a three-expression for-loop (see below) under the name <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for</code>.

<div class="mw-heading mw-heading3"><h3 id="Vectorised_for-loops">Vectorised for-loops</h3></div>

Some languages offer a for-loop that acts as if processing all iterations <a href="Automatic_vectorization" title="Automatic vectorization">in parallel</a>, such as the <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for all</code> keyword in <a href="Fortran_95" class="mw-redirect" title="Fortran 95">Fortran 95</a> which has the interpretation that all <a href="Sides_of_an_equation" title="Sides of an equation">right-hand-side</a> expressions are evaluated before any assignments are made, as distinct from the explicit iteration form. For example, in the <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for</code> statement in the following <a href="Pseudocode" title="Pseudocode">pseudocode</a> fragment, when calculating the new value for <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">A(i)</code>, except for the first (with <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">i = 2</code>) the reference to <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">A(i - 1)</code> will obtain the new value that had been placed there in the previous step. In the <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for all</code> version, however, each calculation refers only to the original, unaltered <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">A</code>.

<pre>for i := 2 : N - 1 do A(i) := [A(i - 1) + A(i) + A(i + 1)] / 3; next i;

for all i := 2 : N - 1 do A(i) := [A(i - 1) + A(i) + A(i + 1)] / 3;

</pre>

The difference may be significant.

Some languages (such as PL/I, Fortran 95) also offer array assignment statements, that enable many for-loops to be omitted. Thus pseudocode such as <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">A:= 0;</code> would set all elements of array A to zero, no matter its size or dimensionality. The example loop could be rendered as

<div class="mw-highlight mw-highlight-lang-fortran mw-content-ltr" dir="ltr"><pre> A(2 : N - 1) := [A(1 : N - 2) + A(2 : N - 1) + A(3 : N)] / 3;

</pre></div>

But whether that would be rendered in the style of the for-loop or the for-all-loop or something else may not be clearly described in the compiler manual.

<div class="mw-heading mw-heading3"><h3 id="Compound_for-loops">Compound for-loops</h3></div>

Introduced with <a href="ALGOL_68" title="ALGOL 68">ALGOL 68</a> and followed by PL/I, this allows the iteration of a loop to be compounded with a test, as in

<pre>for i := 1 : N while A(i) > 0 do etc.

</pre>

That is, a value is assigned to the loop variable i and only if the while expression is true will the loop body be executed. If the result were false the for-loop's execution stops short. Granted that the loop variable's value is defined after the termination of the loop, then the above statement will find the first non-positive element in array A (and if no such, its value will be N + 1), or, with suitable variations, the first non-blank character in a string, and so on.

<div class="mw-heading mw-heading2"><h2 id="Loop_counters">Loop counters</h2></div>

In <a href="Computer_programming" title="Computer programming">computer programming</a>, a loop counter is a control variable that controls the iterations of a loop (a computer <a href="Programming_language" title="Programming language">programming language</a> construct). It is so named because most uses of this construct result in the variable taking on a range of integer values in some orderly sequences (for example., starting at 0 and ending at 10 in increments of 1)

Loop counters change with each iteration of a loop, providing a unique value for each iteration. The loop counter is used to decide when the loop should terminate and for the program flow to continue to the next <a href="Instruction_(computer_science)" class="mw-redirect" title="Instruction (computer science)">instruction</a> after the loop.

A common <a href="Identifier_naming_convention" class="mw-redirect" title="Identifier naming convention">identifier naming convention</a> is for the loop counter to use the variable names i, j, and k (and so on if needed), where i would be the most outer loop, j the next inner loop, etc. The reverse order is also used by some programmers. This style is generally agreed to have originated from the early programming of Fortran, where these variable names beginning with these letters were implicitly declared as having an integer type, and so were obvious choices for loop counters that were only temporarily required. The practice dates back further to <a href="Mathematical_notation" title="Mathematical notation">mathematical notation</a> where <a href="Index_notation" title="Index notation">indices</a> for <a href="Summation" title="Summation">sums</a> and <a href="Multiplication" title="Multiplication">multiplications</a> are often i, j, etc. A variant convention is the use of duplicated letters for the index, ii, jj, and kk, as this allows easier searching and search-replacing than using a single letter.<a href="#cite_note-3">[3]</a>

<div class="mw-heading mw-heading3"><h3 id="Example">Example</h3></div>

An example of C code involving nested for loops, where the loop counter variables are i and j:

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>for (i = 0; i < 100; i++) {

for (j = i; j < 10; j++) {

some_function(i, j);

}

}

</pre></div>

Loops in C can also be used to print the reverse of a word. As:

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>for (i = 0; i < 6; i++) {

scanf("%c", &a[i]);

}

for (i = 4; i >= 0; i--) {

printf("%c", a[i]);

}

</pre></div>

Here, if the input is <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">apple</code>, the output will be <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">elppa</code>.

<div class="mw-heading mw-heading2"><h2 id="Additional_semantics_and_constructs">Additional semantics and constructs</h2></div>

<div class="mw-heading mw-heading3"><h3 id="Use_as_infinite_loops">Use as infinite loops</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Infinite_loop" title="Infinite loop">Infinite loop</a></div>

This C-style for-loop is commonly the source of an <a href="Infinite_loop" title="Infinite loop">infinite loop</a> since the fundamental steps of iteration are completely in the control of the programmer. When infinite loops are intended, this type of for-loop can be used (with empty expressions), such as:

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>for (;;)

//loop body

</pre></div>

This style is used instead of infinite <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">while (1)</code> loops to avoid a <a href="Type_conversion" title="Type conversion">type conversion</a> warning in some C/C++ compilers.<a href="#cite_note-4">[4]</a> Some programmers prefer the more succinct <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for (;;)</code> form over the semantically equivalent but more verbose <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">while (true)</code> form.

<div class="mw-heading mw-heading3"><h3 id="Early_exit_and_continuation">Early exit and continuation</h3></div>

Some languages may also provide other supporting statements, which when present can alter how the for-loop iteration proceeds. Common among these are the <a href="Break_statement" class="mw-redirect" title="Break statement">break</a> and <a href="Control_flow#Continuation_with_next_iteration" title="Control flow">continue</a> statements found in C and its derivatives. The break statement causes the innermost loop to be terminated immediately when executed. The continue statement will move at once to the next iteration without further progress through the loop body for the current iteration. A for statement also terminates when a break, goto, or <a href="Return_statement" title="Return statement">return statement</a> within the statement body is executed.[Wells] Other languages may have similar statements or otherwise provide means to alter the for-loop progress; for example in Fortran 90:

<div class="mw-highlight mw-highlight-lang-fortran mw-content-ltr" dir="ltr"><pre>DO I = 1, N

statements!Executed for all values of "I", up to a disaster if any.

IF (no good) CYCLE! Skip this value of "I", and continue with the next.

Statements!Executed only where goodness prevails.

IF (disaster) EXIT! Abandon the loop.

Statements!While good and, no disaster.

END DO! Should align with the "DO".

</pre></div>

Some languages offer further facilities such as naming the various loop constructs so that with multiple nested loops there is no doubt as to which loop is involved. Fortran 90, for example:

<div class="mw-highlight mw-highlight-lang-fortran mw-content-ltr" dir="ltr"><pre>X1:DO I = 1, N

statements

X2:DO J = 1, M

statements

IF (trouble) CYCLE X1

statements

END DO X2

statements

END DO X1

</pre></div>

Thus, when "trouble" is detected in the inner loop, the CYCLE X1 (not X2) means that the skip will be to the next iteration for I, not J. The compiler will also be checking that each END DO has the appropriate label for its position: this is not just a documentation aid. The programmer must still code the problem correctly, but some possible blunders will be blocked.

<div class="mw-heading mw-heading3"><h3 id="Loop_variable_scope_and_semantics">Loop variable scope and semantics</h3></div>

Different languages specify different rules for what value the loop variable will hold on termination of its loop, and indeed some hold that it "becomes undefined". This permits a <a href="Compiler" title="Compiler">compiler</a> to generate code that leaves any value in the loop variable, or perhaps even leaves it unchanged because the loop value was held in a register and never stored in memory. Actual behavior may even vary according to the compiler's optimization settings, as with the Honeywell Fortran66 compiler.

In some languages (not <a href="C_(programming_language)" title="C (programming language)">C</a> or <a href="C%2B%2B" title="C++">C++</a>) the loop variable is <a href="Immutable_object" title="Immutable object">immutable</a> within the scope of the loop body, with any attempt to modify its value being regarded as a semantic error. Such modifications are sometimes a consequence of a programmer error, which can be very difficult to identify once made. However, only overt changes are likely to be detected by the compiler. Situations, where the address of the loop variable is passed as an argument to a <a href="Subroutine" class="mw-redirect" title="Subroutine">subroutine</a>, make it very difficult to check because the routine's behavior is in general unknowable to the compiler unless the language supports procedure signatures and argument intents. Some examples in the style of pre-Fortran-90:

I = 7 !Overt adjustment of the loop variable. Compiler should complain

Z = ADJUST(I) !Function "ADJUST" might alter "I", to uncertain effect.

PRINT *, (A(I), B(I), I = 1, N, 2) !Implicit for-loop to print odd elements of arrays A and B, reusing "I"... Compiler should complain.

END DO! How many times will the loop be executed?

</pre></div>

A common approach is to calculate the iteration count at the start of a loop (with careful attention to overflow as in <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for i:= 0: 65535 do ... ;</code> in sixteen-bit integer arithmetic) and with each iteration decrement this count while also adjusting the value of I: double counting results. However, adjustments to the value of I within the loop will not change the number of iterations executed.

Still, another possibility is that the code generated may employ an auxiliary variable as the loop variable, possibly held in a machine register, whose value may or may not be copied to I on each iteration. Again, modifications of I would not affect the control of the loop, but now a disjunction is possible: within the loop, references to the value of I might be to the (possibly altered) current value of I or to the auxiliary variable (held safe from improper modification) and confusing results are guaranteed. For instance, within the loop a reference to element I of an array would likely employ the auxiliary variable (especially if it were held in a machine register), but if I is a parameter to some routine (for instance, a print-statement to reveal its value), it would likely be a reference to the proper variable I instead. It is best to avoid such possibilities.

<div class="mw-heading mw-heading4"><h4 id="Adjustment_of_bounds">Adjustment of bounds</h4></div>

Just as the index variable might be modified within a for-loop, so also may its bounds and direction. But to uncertain effect. A compiler may prevent such attempts, they may have no effect, or they might even work properly - though many would declare that to do so would be wrong. Consider a statement such as

<pre>for i := first : last : step do

A(i) := A(i) / A(last);

</pre>

If the approach to compiling such a loop was to be the evaluation of first, last and step and the calculation of an iteration count via something like <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">(last - first)/step</code> once only at the start, then if those items were simple variables and their values were somehow adjusted during the iterations, this would have no effect on the iteration count even if the element selected for division by <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">A(last)</code> changed.

<div class="mw-heading mw-heading3"><h3 id="List_of_value_ranges">List of value ranges</h3></div>

ALGOL 60, PL/I, and ALGOL 68, allow loops in which the loop variable is iterated over a list of ranges of values instead of a single range. The following PL/I example will execute the loop with six values of i: 1, 7, 12, 13, 14, 15:

<div class="mw-highlight mw-highlight-lang-rexx mw-content-ltr" dir="ltr"><pre>do i = 1, 7, 12 to 15;

/*statements*/

end;

</pre></div>

<div class="mw-heading mw-heading2"><h2 id="Equivalence_with_while-loops">Equivalence with while-loops</h2></div>

A for-loop is generally equivalent to a while-loop:

<pre>factorial := 1

for counter from 2 to 5

factorial := factorial * counter

counter:= counter - 1

print counter + "! equals " + factorial

</pre>

Is equivalent to:

<pre>factorial := 1

counter := 1

while counter < 5

counter := counter + 1

factorial := factorial * counter

print counter + "! equals " + factorial

</pre>

As demonstrated by the output of the variables.

<div class="mw-heading mw-heading2"><h2 id="Timeline_of_the_for-loop_syntax_in_various_programming_languages">Timeline of the for-loop syntax in various programming languages</h2></div>

Given an action that must be repeated, for instance, five times, different languages' for-loops will be written differently. The syntax for a three-expression for-loop is nearly identical in all languages that have it, after accounting for different styles of block termination and so on.

<div class="mw-heading mw-heading3"><h3 id="1957:_FORTRAN">1957: FORTRAN</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Fortran" title="Fortran">Fortran</a></div>

Fortran's equivalent of the for loop is the DO loop,

using the keyword do instead of for,

The syntax of Fortran's DO loop is:

<div class="mw-highlight mw-highlight-lang-fortranfixed mw-content-ltr" dir="ltr"><pre> DO label counter = first, last, step

statements

label statement

</pre></div>

The following two examples behave equivalently to the three argument for-loop in other languages,

initializing the counter variable to 1, incrementing by 1 each iteration of the loop, and stopping at five (inclusive).

<div class="mw-highlight mw-highlight-lang-fortranfixed mw-content-ltr" dir="ltr"><pre> DO 9, ICOUNT = 1, 5, 1

WRITE (6,8) ICOUNT

8 FORMAT( I2 )

9 CONTINUE

</pre></div>

As of Fortran 90, block structured END DO was added to the language. With this, the end of loop label became optional:

<div class="mw-highlight mw-highlight-lang-fortran mw-content-ltr" dir="ltr"><pre>do icounter = 1, 5

write(*, '(i2)') icounter

end do

</pre></div>

The step part may be omitted if the step is one. Example:

<div class="mw-highlight mw-highlight-lang-fortranfixed mw-content-ltr" dir="ltr"><pre>* DO loop example.

PROGRAM MAIN

INTEGER SUMSQ

SUMSQ = 0

DO 199 I = 1, 9999999

IF (SUMSQ.GT.1000) GO TO 200

199 SUMSQ = SUMSQ + I**2

200 PRINT 206, SUMSQ

206 FORMAT( I2 )

END

</pre></div>

In Fortran 90, the GO TO may be avoided by using an EXIT statement.

<div class="mw-highlight mw-highlight-lang-fortranfixed mw-content-ltr" dir="ltr"><pre>* DO loop example.

program main

implicit none

integer:: sumsq

integer:: i

sumsq = 0

do i = 1, 9999999

if (sumsq > 1000) exit

sumsq = sumsq + i**2

end do

print *, sumsq

end program

</pre></div>

Alternatively, a DO - WHILE construct could be used:

<div class="mw-highlight mw-highlight-lang-fortranfixed mw-content-ltr" dir="ltr"><pre> program main

implicit none

integer:: sumsq

integer:: i

sumsq = 0

i = 0

do while (sumsq <= 1000)

i = i+1

end do

end program

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="1958:_ALGOL">1958: ALGOL</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="ALGOL_58" title="ALGOL 58">ALGOL 58</a></div>

ALGOL 58 introduced the <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for</code> statement, using the form as Superplan:

<pre> FOR Identifier = Base (Difference) Limit

</pre>

For example to print 0 to 10 incremented by 1:

<pre>FOR x = 0 (1) 10 BEGIN

PRINT (FL) = x END

</pre>

<div class="mw-heading mw-heading3"><h3 id="1960:_COBOL">1960: COBOL</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="COBOL" title="COBOL">COBOL</a></div>

<a href="COBOL" title="COBOL">COBOL</a> was formalized in late 1959 and has had many elaborations. It uses the PERFORM verb which has many options. Originally all loops had to be out-of-line with the iterated code occupying a separate paragraph. Ignoring the need for declaring and initializing variables, the COBOL equivalent of a for-loop would be.

<div class="mw-highlight mw-highlight-lang-cobol mw-content-ltr" dir="ltr"><pre> PERFORM SQ-ROUTINE VARYING I FROM 1 BY 1 UNTIL I > 1000

SQ-ROUTINE

ADD I**2 TO SUM-SQ.

</pre></div>

In the 1980s, the addition of in-line loops and <a href="Structured_programming" title="Structured programming">structured programming</a> statements such as END-PERFORM resulted in a for-loop with a more familiar structure.

<div class="mw-highlight mw-highlight-lang-cobol mw-content-ltr" dir="ltr"><pre> PERFORM VARYING I FROM 1 BY 1 UNTIL I > 1000

ADD I**2 TO SUM-SQ.

END-PERFORM

</pre></div>

If the PERFORM verb has the optional clause TEST AFTER, the resulting loop is slightly different: the loop body is executed at least once, before any test.

<div class="mw-heading mw-heading3"><h3 id="1964:_BASIC">1964: BASIC</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="BASIC" title="BASIC">BASIC</a></div>

In <a href="BASIC" title="BASIC">BASIC</a>, a loop is sometimes named a for-next loop.

<div class="mw-highlight mw-highlight-lang-basic mw-content-ltr" dir="ltr"><pre>10 REM THIS FOR LOOP PRINTS ODD NUMBERS FROM 1 TO 15

20 FOR I = 1 TO 15 STEP 2

30 PRINT I

40 NEXT I

</pre></div>

The end-loop marker specifies the name of the index variable, which must correspond to the name of the index variable at the start of the for-loop. Some languages (PL/I, Fortran 95, and later) allow a statement label at the start of a for-loop that can be matched by the compiler against the same text on the corresponding end-loop statement. Fortran also allows the <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">EXIT</code> and <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">CYCLE</code> statements to name this text; in a nest of loops, this makes clear which loop is intended. However, in these languages, the labels must be unique, so successive loops involving the same index variable cannot use the same text nor can a label be the same as the name of a variable, such as the index variable for the loop.

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="PL/I" title="PL/I">PL/I</a></div>

<div class="mw-highlight mw-highlight-lang-rexx mw-content-ltr" dir="ltr"><pre>do counter = 1 to 5 by 1; /* "by 1" is the default if not specified */

/*statements*/;

end;

</pre></div>

The LEAVE statement may be used to exit the loop. Loops can be <a href="Label_(computer_science)" title="Label (computer science)">labeled</a>, and leave may leave a specific labeled loop in a group of nested loops. Some PL/I dialects include the ITERATE statement to terminate the current loop iteration and begin the next.

<div class="mw-heading mw-heading3"><h3 id="1968:_ALGOL_68">1968: ALGOL 68</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="ALGOL_68" title="ALGOL 68">ALGOL 68</a></div>

ALGOL 68 has what was considered the universal loop, the full syntax is:

<pre>FOR i FROM 1 BY 2 TO 3 WHILE i≠4 DO ~ OD

</pre>

Further, the single iteration range could be replaced by a list of such ranges. There are several unusual aspects of the construct

<ul><li>only the <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">do ~ od</code> portion was compulsory, in which case the loop will iterate indefinitely.</li>

<li>thus the clause <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">to 100 do ~ od</code>, will iterate exactly 100 times.</li>

<li>The <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">while</code> syntactic element allowed a programmer to break from a <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for</code> loop early, as in:</li></ul>

<pre>INT sum sq := 0;

FOR i

WHILE

print(("So far:", i, new line)); # Interposed for tracing purposes. #

sum sq ≠ 70↑2 # This is the test for the WHILE #

sum sq +:= i↑2

</pre>

Subsequent extensions to the standard ALGOL 68 allowed the <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">to</code> syntactic element to be replaced with <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">upto</code> and <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">downto</code> to achieve a small optimization. The same compilers also incorporated:

<dl><dt><code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">until</code></dt>

<dd>for late loop termination.</dd>

<dt><code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">foreach</code></dt>

<dd>for working on arrays in <a href="Parallel_computing" title="Parallel computing">parallel</a>.</dd></dl>

<div class="mw-heading mw-heading3"><h3 id="1970:_Pascal">1970: Pascal</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Pascal_(programming_language)" title="Pascal (programming language)">Pascal (programming language)</a></div>

<div class="mw-highlight mw-highlight-lang-pascal mw-content-ltr" dir="ltr"><pre>for Counter:= 1 to 5 do

(*statement*);

</pre></div>

Decrementing (counting backwards) is using <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">downto</code> keyword instead of <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">to</code>, as in:

<div class="mw-highlight mw-highlight-lang-pascal mw-content-ltr" dir="ltr"><pre>for Counter:= 5 down to 1 do

(*statement*);

</pre></div>

The numeric range for-loop varies somewhat more.

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="C_(programming_language)" title="C (programming language)">C (programming language)</a>, <a href="C%2B%2B" title="C++">C++</a>, and <a href="C_syntax#Iteration_statements" title="C syntax">C syntax § Iteration statements</a></div>

statement

</pre></div>

The statement is often a block statement; an example of this would be:

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>//Using for-loops to add numbers 1 - 5

int sum = 0;

for (int i = 1; i <= 5; ++i) {

sum += i;

}

</pre></div>

The ISO/IEC 9899:1999 publication (commonly known as <a href="C99" title="C99">C99</a>) also allows initial declarations in <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">for</code> loops. All three sections in the for loop are optional, with an empty condition equivalent to true.

<div class="mw-heading mw-heading3"><h3 id="1972:_Smalltalk">1972: Smalltalk</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Smalltalk" title="Smalltalk">Smalltalk</a></div>

<div class="mw-highlight mw-highlight-lang-smalltalk mw-content-ltr" dir="ltr"><pre>1 to: 5 do: [ :counter | "statements" ]

</pre></div>

Contrary to other languages, in <a href="Smalltalk" title="Smalltalk">Smalltalk</a> a for-loop is not a <a href="Language_construct" title="Language construct">language construct</a> but is defined in the class Number as a method with two parameters, the end value and a <a href="Closure_(computer_science)" class="mw-redirect" title="Closure (computer science)">closure</a>, using self as start value.

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Ada_(programming_language)" title="Ada (programming language)">Ada (programming language)</a></div>

<div class="mw-highlight mw-highlight-lang-ada mw-content-ltr" dir="ltr"><pre>for Counter in 1 .. 5 loop

-- statements

end loop;

</pre></div>

The exit statement may be used to exit the loop. Loops can be labeled, and exit may leave a specifically labeled loop in a group of nested loops:

<div class="mw-highlight mw-highlight-lang-ada mw-content-ltr" dir="ltr"><pre>Counting:

For Counter in 1 .. 5 loop

Triangle:

for Secondary_Index in 2 .. Counter loop

-- statements

exit Counting;

-- statements

end loop Triangle;

end loop Counting;

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="1980:_Maple">1980: Maple</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Maple_(software)" title="Maple (software)">Maple (software)</a></div>

Maple has two forms of for-loop, one for iterating over a range of values, and the other for iterating over the contents of a container. The value range form is as follows:

<pre>for i from f by b to t while w do

# loop body

od;

</pre>

All parts except <code>do</code> and <code>od</code> are optional. The <code> for I</code> part, if present, must come first. The remaining parts (<code>from f</code>, <code>by b</code>, <code>to t</code>, <code>while w</code>) can appear in any order.

Iterating over a container is done using this form of loop:

<pre>for e in c while w do

# loop body

od;

</pre>

The <code> in c</code> clause specifies the container, which may be a list, set, sum, product, unevaluated function, array, or object implementing an iterator.

A for-loop may be terminated by <code>od</code>, <code>end</code>, or <code>end do</code>.

<div class="mw-heading mw-heading3"><h3 id="1982:_Maxima_CAS">1982: Maxima CAS</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Maxima_(software)" title="Maxima (software)">Maxima (software)</a></div>

In Maxima CAS, one can use also integer values:

<div class="mw-highlight mw-highlight-lang-maxima mw-content-ltr" dir="ltr"><pre>for x:0.5 step 0.1 thru 0.9 do

/* "Do something with x" */

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="1982:_PostScript">1982: PostScript</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="PostScript" title="PostScript">PostScript</a></div>

The for-loop, written as <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">[initial] [increment] [limit] { ... } for</code> initializes an internal variable, and executes the body as long as the internal variable is not more than the limit (or not less, if the increment is negative) and, at the end of each iteration, increments the internal variable. Before each iteration, the value of the internal variable is pushed onto the stack.<a href="#cite_note-5">[5]</a>

<div class="mw-highlight mw-highlight-lang-applescript mw-content-ltr" dir="ltr"><pre>1 1 6 {STATEMENTS} for

</pre></div>

There is also a simple repeat loop.

The repeat-loop, written as <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">X { ... } repeat</code>, repeats the body exactly X times.<a href="#cite_note-6">[6]</a>

<div class="mw-highlight mw-highlight-lang-applescript mw-content-ltr" dir="ltr"><pre>5 { STATEMENTS } repeat

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="1983:_Ada_83_and_above">1983: Ada 83 and above</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Ada_(programming_language)" title="Ada (programming language)">Ada (programming language)</a></div>

<div class="mw-highlight mw-highlight-lang-ada mw-content-ltr" dir="ltr"><pre>procedure Main is

Sum_Sq : Integer := 0;

begin

for I in 1 .. 9999999 loop

if Sum_Sq <= 1000 then

Sum_Sq := Sum_Sq + I**2

end if;

end loop;

end;

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="1984:_MATLAB">1984: MATLAB</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="MATLAB" title="MATLAB">MATLAB</a></div>

<div class="mw-highlight mw-highlight-lang-matlab mw-content-ltr" dir="ltr"><pre>for n = 1:5

-- statements

end

</pre></div>

After the loop, <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">n</code> would be 5 in this example.

As <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">i</code> is used for the <a href="Imaginary_unit" title="Imaginary unit">Imaginary unit</a>, its use as a loop variable is discouraged.

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Perl" title="Perl">Perl</a></div>

<div class="mw-highlight mw-highlight-lang-perl mw-content-ltr" dir="ltr"><pre>for ($counter = 1; $counter <= 5; $counter++) { # implicitly or predefined variable

# statements;

}

for (my $counter = 1; $counter <= 5; $counter++) { # variable private to the loop

# statements;

}

for (1..5) { # variable implicitly called $_; 1..5 creates a list of these 5 elements

# statements;

}

statement for 1..5; # almost same (only 1 statement) with natural language order

for my $counter (1..5) { # variable private to the loop

# statements;

}

</pre></div>

"<a href="There's_more_than_one_way_to_do_it" class="mw-redirect" title="There's more than one way to do it">There's more than one way to do it</a>" is a Perl programming motto.

<div class="mw-heading mw-heading3"><h3 id="1988:_Mathematica">1988: Mathematica</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Wolfram_Mathematica" class="mw-redirect" title="Wolfram Mathematica">Wolfram Mathematica</a> and <a href="Wolfram_Language" title="Wolfram Language">Wolfram Language</a></div>

The construct corresponding to most other languages' for-loop is named Do in Mathematica.

<div class="mw-highlight mw-highlight-lang-ruby mw-content-ltr" dir="ltr"><pre>Do[f[x], {x, 0, 1, 0.1}]

</pre></div>

Mathematica also has a For construct that mimics the for-loop of C-like languages.

<div class="mw-highlight mw-highlight-lang-ruby mw-content-ltr" dir="ltr"><pre>For[x= 0 , x <= 1, x += 0.1,

f[x]

]

</pre></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Bash_(Unix_shell)" title="Bash (Unix shell)">Bash (Unix shell)</a></div>

<div class="mw-highlight mw-highlight-lang-bash mw-content-ltr" dir="ltr"><pre># first form

for i in 1 2 3 4 5

do

# must have at least one command in a loop

echo $i # just print the value of i

done

</pre></div>

<div class="mw-highlight mw-highlight-lang-bash mw-content-ltr" dir="ltr"><pre># second form

for (( i = 1; i <= 5; i++ ))

do

# must have at least one command in a loop

echo $i # just print the value of i

done

</pre></div>

An empty loop (i.e., one with no commands between <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">do</code> and <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">done</code>) is a syntax error. If the above loops contained only comments, execution would result in the message "syntax error near unexpected token 'done'".

<div class="mw-heading mw-heading3"><h3 id="1990:_Haskell">1990: Haskell</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Haskell" title="Haskell">Haskell</a></div>

In Haskell98, the function mapM_ maps a <a href="Monad_(functional_programming)" title="Monad (functional programming)">monadic</a> function over a list, as

<div class="mw-highlight mw-highlight-lang-haskell mw-content-ltr" dir="ltr"><pre>mapM_ print [4, 3 .. 1]

-- prints

-- 4

-- 3

-- 2

-- 1

</pre></div>

The function mapM collects each iteration result in a list:

<div class="mw-highlight mw-highlight-lang-haskell mw-content-ltr" dir="ltr"><pre>result_list <- mapM (\ indx -> do{ print indx; return (indx - 1) }) [1..4]

-- prints

-- 1

-- 2

-- 3

-- 4

-- result_list is [0,1,2,3,4]

</pre></div>

Haskell2010 adds functions forM_ and forM, which are equivalent to mapM_ and mapM, but with their arguments flipped:

<div class="mw-highlight mw-highlight-lang-haskell mw-content-ltr" dir="ltr"><pre>forM_ [0..3] $ \ indx -> do

print indx

-- prints

-- 0

-- 1

-- 2

-- 3

result_list <- forM ['a'..'d'] $ \ indx -> do

print indx

return indx

-- prints

-- 'a'

-- 'b'

-- 'c'

-- 'd'

-- result_list is ['a','b','c','d']

</pre></div>

When compiled with optimization, none of the expressions above will create lists. But, to save the space of the [1..5] list if optimization is turned off, a forLoop_ function could be defined as

<div class="mw-highlight mw-highlight-lang-haskell mw-content-ltr" dir="ltr"><pre>import Control.Monad as M

forLoop_ :: Monad m => a -> (a -> Bool) -> (a -> a) -> (a -> m ()) -> m ()

forLoop_ startIndx test next f = theLoop startIndx

where

theLoop indx = M.when (test indx) $ do

f indx

theLoop (next indx)

</pre></div>

and used as

<div class="mw-highlight mw-highlight-lang-haskell mw-content-ltr" dir="ltr"><pre>forLoopM_ (0::Int) (< len) (+1) $ \indx -> do

-- statements

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="1991:_Oberon-2,_Oberon-07,_Component_Pascal">1991: Oberon-2, Oberon-07, Component Pascal</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Oberon_(programming_language)" title="Oberon (programming language)">Oberon (programming language)</a>, <a href="Oberon-2" title="Oberon-2">Oberon-2</a>, and <a href="Component_Pascal" title="Component Pascal">Component Pascal</a></div>

<div class="mw-highlight mw-highlight-lang-modula2 mw-content-ltr" dir="ltr"><pre>FOR Counter:= 1 TO 5 DO

(* statement sequence *)

END

</pre></div>

In the original Oberon language, the for-loop was omitted in favor of the more general Oberon loop construct. The for-loop was reintroduced in Oberon-2.

<div class="mw-heading mw-heading3"><h3 id="1991:_Python">1991: Python</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Python_(programming_language)" title="Python (programming language)">Python (programming language)</a></div>

Python does not contain the classical for loop, rather a <code>foreach</code> loop is used to iterate over the output of the built-in <code>range()</code> function which returns an iterable sequence of integers.<div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>for i in range(1, 6): # gives i values from 1 to 5 inclusive (but not 6)

# statements

print(i)

# if we want 6 we must do the following

for i in range(1, 6 + 1): # gives i values from 1 to 6

# statements

print(i)

</pre></div>Using <code>range(6)</code> would run the loop from 0 to 5.

When the loop variable is not needed, it is common practice to use an underscore (<code>_</code>) as a placeholder. This convention signals to other developers that the variable will not be used inside the loop. For example:

<div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>for _ in range(5):

print("Hello")

</pre></div>

This will print “Hello” five times without using the loop variable.

<div class="mw-heading mw-heading3"><h3 id="1993:_AppleScript">1993: AppleScript</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="AppleScript" title="AppleScript">AppleScript</a></div>

<div class="mw-highlight mw-highlight-lang-applescript mw-content-ltr" dir="ltr"><pre>repeat with i from 1 to 5

-- statements

log i

end repeat

</pre></div>

It can also iterate through a list of items, similar to what can be done with arrays in other languages:

<div class="mw-highlight mw-highlight-lang-applescript mw-content-ltr" dir="ltr"><pre>set x to {1, "waffles", "bacon", 5.1, false}

repeat with i in x

log i

end repeat

</pre></div>

A <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">exit repeat</code> may also be used to exit a loop at any time. Unlike other languages, AppleScript currently has no command to continue to the next iteration of a loop.

<div class="mw-heading mw-heading3"><h3 id="1993:_Crystal">1993: Crystal</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Crystal_(programming_language)" title="Crystal (programming language)">Crystal (programming language)</a></div>

<div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>for i = start, stop, interval do

-- statements

end

</pre></div>

So, this code <div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>for i = 1, 5, 2 do

print(i)

end

</pre></div> will print:

<div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>1 3 5

</pre></div>

For-loops can also loop through a table using <div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>ipairs()

</pre></div> to iterate numerically through arrays and <div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>pairs()

</pre></div> to iterate randomly through dictionaries.

Generic for-loop making use of closures:

<div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>for name, phone, and address in contacts() do

-- contacts() must be an iterator function

end

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="1995:_ColdFusion_Markup_Language_(CFML)">1995: ColdFusion Markup Language (CFML)</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="ColdFusion_Markup_Language" title="ColdFusion Markup Language">ColdFusion Markup Language</a></div>

<div class="mw-heading mw-heading4"><h4 id="Script_syntax">Script syntax</h4></div>

Simple index loop:

<div class="mw-highlight mw-highlight-lang-cfs mw-content-ltr" dir="ltr"><pre>for (i = 1; i <= 5; i++) {

// statements

}

</pre></div>

Using an array:

<div class="mw-highlight mw-highlight-lang-cfs mw-content-ltr" dir="ltr"><pre>for (i in [1,2,3,4,5]) {

// statements

}

</pre></div>

Using a list of string values:

<div class="mw-highlight mw-highlight-lang-cfs mw-content-ltr" dir="ltr"><pre>loop index="i" list="1;2,3;4,5" delimiters=",;" {

// statements

}

</pre></div>

The above <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">list</code> example is only available in the dialect of CFML used by <a href="Lucee" title="Lucee">Lucee</a> and <a href="Railo" title="Railo">Railo</a>.

<div class="mw-heading mw-heading4"><h4 id="Tag_syntax">Tag syntax</h4></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Tag_(programming)" title="Tag (programming)">Tag (programming)</a></div>

Simple index loop:

</cfloop>

</pre></div>

Using an array:

</cfloop>

</pre></div>

Using a "list" of string values:

</cfloop>

</pre></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Java_(programming_language)" title="Java (programming language)">Java (programming language)</a></div>

<div class="mw-highlight mw-highlight-lang-java mw-content-ltr" dir="ltr"><pre>for (int i = 0; i < 5; i++) {

//perform functions within the loop;

//can use the statement 'break;' to exit early;

//can use the statement 'continue;' to skip the current iteration

}

</pre></div>

For the extended for-loop, see <a href="Foreach_loop#Java" title="Foreach loop">Foreach loop § Java</a>.

<div class="mw-heading mw-heading3"><h3 id="1995:_JavaScript">1995: JavaScript</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="JavaScript" title="JavaScript">JavaScript</a></div>

JavaScript supports C-style "three-expression" loops. The <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">break</code> and <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">continue</code> statements are supported inside loops.

<div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>for (var i = 0; i < 5; i++) {

// ...

}

</pre></div>

Alternatively, it is possible to iterate over all keys of an array.

<div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>for (var key in array) { // also works for assoc. arrays

// use array[key]

...

}

</pre></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="PHP" title="PHP">PHP</a></div>

This prints out a triangle of *

<div class="mw-highlight mw-highlight-lang-php mw-content-ltr" dir="ltr"><pre>for ($i = 0; $i <= 5; $i++) {

for ($j = 0; $j <= $i; $j++) {

echo "*";

}

echo " \n";

}

</pre></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Ruby_(programming_language)" title="Ruby (programming language)">Ruby (programming language)</a></div>

<div class="mw-highlight mw-highlight-lang-ruby mw-content-ltr" dir="ltr"><pre>for the counter in 1..5

# statements

end

5.times do |counter| # counter iterates from 0 to 4

# statements

end

1.upto(5) do |counter|

# statements

end

</pre></div>

<a href="Ruby_programming_language" class="mw-redirect" title="Ruby programming language">Ruby</a> has several possible syntaxes, including the above samples.

<div class="mw-heading mw-heading3"><h3 id="1996:_OCaml">1996: OCaml</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="OCaml" title="OCaml">OCaml</a></div>

See expression syntax.<a href="#cite_note-7">[7]</a>

<div class="mw-highlight mw-highlight-lang-ocaml mw-content-ltr" dir="ltr"><pre> (* for_statement:= "for" ident '=' expr ( "to" ∣ "down to" ) expr "do" expr "done" *)

for i = 1 to 5 do

(* statements *)

done ;;

for j = 5 down to 0 do

(* statements *)

done ;;

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="1998:_ActionScript_3">1998: ActionScript 3</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="ActionScript" title="ActionScript">ActionScript</a></div>

<div class="mw-highlight mw-highlight-lang-actionscript3 mw-content-ltr" dir="ltr"><pre>for (var counter:uint = 1; counter <= 5; counter++){

//statement;

}

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="2008:_Small_Basic">2008: Small Basic</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Microsoft_Small_Basic" title="Microsoft Small Basic">Microsoft Small Basic</a></div>

<div class="mw-highlight mw-highlight-lang-vbnet mw-content-ltr" dir="ltr"><pre>For i = 1 To 10

' Statements

EndFor

</pre></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Nim_(programming_language)" title="Nim (programming language)">Nim (programming language)</a></div>

<a href="Nim_(programming_language)" title="Nim (programming language)">Nim</a> has a <code>foreach</code>-type loop and various operations for creating iterators.<a href="#cite_note-8">[8]</a>

<div class="mw-highlight mw-highlight-lang-nim mw-content-ltr" dir="ltr"><pre>for i in 5 .. 10:

# statements

</pre></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Go_(programming_language)" title="Go (programming language)">Go (programming language)</a></div>

<div class="mw-highlight mw-highlight-lang-go mw-content-ltr" dir="ltr"><pre>for i := 0; i <= 10; i++ {

// statements

}

</pre></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Rust_(programming_language)" title="Rust (programming language)">Rust (programming language)</a></div>

<div class="mw-highlight mw-highlight-lang-rust mw-content-ltr" dir="ltr"><pre>for i in 0..10 {

// statements

}

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="2012:_Julia">2012: Julia</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Julia_(programming_language)" title="Julia (programming language)">Julia (programming language)</a></div>

<div class="mw-highlight mw-highlight-lang-julia mw-content-ltr" dir="ltr"><pre>for j = 1:10

# statements

end

</pre></div>

<ul><li><a href="Do_while_loop" title="Do while loop">Do while loop</a></li>

<li><a href="Foreach" class="mw-redirect" title="Foreach">Foreach</a></li>

<li><a href="While_loop" title="While loop">While loop</a></li>

<li><a href="Primitive_recursive_function" title="Primitive recursive function">Primitive recursive function</a></li>

<li><a href="General_recursive_function" title="General recursive function">General recursive function</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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/* end https://en.wikipedia.org/ */

</style><cite id="CITEREFWirth1973" class="citation book cs1"><a href="Niklaus_Wirth" title="Niklaus Wirth">Wirth, Niklaus</a> (1973). "Preface". Systematic Programming: An Introduction. Prentice-Hall. pp. xiii. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0138803692</bdi>.</cite>

</li>

<li id="cite_note-ken-2"><a href="#cite_ref-ken_2-0">^</a> <cite id="CITEREFThompson" class="citation audio-visual cs1"><a href="Ken_Thompson" title="Ken Thompson">Thompson, Ken</a>. <a rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=EY6q5dv_B-o&t=2330">VCF East 2019 – Brian Kernighan interviews Ken Thompson</a>. <a href="YouTube" title="YouTube">YouTube</a>. <a rel="nofollow" class="external text" href="https://ghostarchive.org/varchive/youtube/20211212/EY6q5dv_B-o">Archived</a> from the original on 2021-12-12. Retrieved 2020-11-16. <q>I saw Johnson's semicolon version of the for loop and I put that in [B], I stole it.</q></cite>

</li>

<li id="cite_note-3"><a href="#cite_ref-3">^</a> <a rel="nofollow" class="external free" href="http://www.knosof.co.uk/vulnerabilities/loopcntrl.pdf">http://www.knosof.co.uk/vulnerabilities/loopcntrl.pdf</a> Analysis of loop control variables in C

</li>

<li id="cite_note-4"><a href="#cite_ref-4">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://msdn.microsoft.com/en-us/library/6t66728h.aspx">"Compiler Warning (level 4) C4127"</a>. Microsoft. Retrieved 29 June 2011.</cite>

</li>

<li id="cite_note-5"><a href="#cite_ref-5">^</a> <cite class="citation book cs1">PostScript Language Reference. Addison-Wesley Publishing Company. 1999. p. 596. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-201-37922-8</bdi>.</cite>

</li>

<li id="cite_note-6"><a href="#cite_ref-6">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://pscript.dubmun.com/tutorial4.html">"PostScript Tutorial - Loops"</a>.</cite>

</li>

<li id="cite_note-7"><a href="#cite_ref-7">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://archive.today/20130412180254/http://caml.inria.fr/pub/docs/manual-ocaml-4.00/expr.html">"OCaml expression syntax"</a>. Archived from <a rel="nofollow" class="external text" href="http://caml.inria.fr/pub/docs/manual-ocaml-4.00/expr.html">the original</a> on 2013-04-12. Retrieved 2013-03-19.</cite>

</li>

<li id="cite_note-8"><a href="#cite_ref-8">^</a> <a rel="nofollow" class="external free" href="https://nim-lang.org/docs/system.html#...i%2CT%2CT">https://nim-lang.org/docs/system.html#...i%2CT%2CT</a> ".. iterator"

</li>

</ol></div></div></div><div><div class="zim-footer">

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