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diff --git a/devdocs/c/language%2Fwhile.html b/devdocs/c/language%2Fwhile.html new file mode 100644 index 00000000..72920439 --- /dev/null +++ b/devdocs/c/language%2Fwhile.html @@ -0,0 +1,59 @@ + <h1 id="firstHeading" class="firstHeading">while loop</h1> <p>Executes a <span class="t-spar">statement</span> repeatedly, until the value of <span class="t-spar">expression</span> becomes equal to zero. The test takes place before each iteration.</p> +<h3 id="Syntax"> Syntax</h3> <table class="t-sdsc-begin"> <tr class="t-sdsc"> <td class="t-sdsc-nopad"> <span class="t-spar">attr-spec-seq</span><span class="t-mark">(optional)</span> <code>while (</code> <span class="t-spar">expression</span> <code>)</code> <span class="t-spar">statement</span> </td> <td class="t-sdsc-nopad"> </td> <td class="t-sdsc-nopad"> </td> +</tr> +</table> <table class="t-par-begin"> <tr class="t-par"> <td> <span class="t-spar">expression</span> </td> <td> - </td> <td> any <a href="expressions" title="c/language/expressions">expression</a> of <a href="type#Type_groups" title="c/language/type">scalar type</a>. This expression is evaluated before each iteration, and if it compares equal to zero, the loop is exited. </td> +</tr> <tr class="t-par"> <td> <span class="t-spar">statement</span> </td> <td> - </td> <td> any <a href="statements" title="c/language/statements">statement</a>, typically a compound statement, which serves as the body of the loop </td> +</tr> <tr class="t-par"> <td> <span class="t-spar">attr-spec-seq</span> </td> <td> - </td> <td> <span class="t-mark-rev t-since-c23">(C23)</span>optional list of <a href="attributes" title="c/language/attributes">attributes</a>, applied to the loop statement </td> +</tr> +</table> <h3 id="Explanation"> Explanation</h3> <p>A <code>while</code> statement causes the <span class="t-spar">statement</span> (also called <i>the loop body</i>) to be executed repeatedly until the <span class="t-spar">expression</span> (also called <i>controlling expression</i>) compares equal to zero. The repetition occurs regardless of whether the loop body is entered normally or by a <a href="goto" title="c/language/goto">goto</a> into the middle of <span class="t-spar">statement</span>.</p> +<p>The evaluation of <span class="t-spar">expression</span> takes place before each execution of <span class="t-spar">statement</span> (unless entered by a goto). If the controlling expression needs to be evaluated after the loop body, the <a href="do" title="c/language/do">do-while loop</a> may be used.</p> +<p>If the execution of the loop needs to be terminated at some point, <a href="break" title="c/language/break"> break statement</a> can be used as a terminating statement.</p> +<p>If the execution of the loop needs to be continued at the end of the loop body, <a href="continue" title="c/language/continue"> continue statement</a> can be used as a shortcut.</p> +<p>A program with an endless loop has undefined behavior if the loop has no observable behavior (I/O, volatile accesses, atomic or synchronization operation) in any part of its <span class="t-spar">statement</span> or <span class="t-spar">expression</span>. This allows the compilers to optimize out all unobservable loops without proving that they terminate. The only exceptions are the loops where <span class="t-spar">expression</span> is a constant expression; <code>while(true)</code> is always an endless loop.</p> +<table class="t-rev-begin"> <tr class="t-rev t-since-c99"> +<td> <p>As with all other selection and iteration statements, the while statement establishes <a href="scope" title="c/language/scope">block scope</a>: any identifier introduced in the <span class="t-spar">expression</span> goes out of scope after the <span class="t-spar">statement</span>.</p> +</td> <td><span class="t-mark-rev t-since-c99">(since C99)</span></td> +</tr> </table> <h3 id="Notes"> Notes</h3> <p>Boolean and pointer expressions are often used as loop controlling expressions. The boolean value <code>false</code> and the null pointer value of any pointer type compare equal to zero.</p> +<h3 id="Keywords"> Keywords</h3> <p><a href="../keyword/while" title="c/keyword/while"><code>while</code></a></p> +<h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include <stdio.h> +#include <stdlib.h> +#include <string.h> +enum { SIZE = 8 }; +int main(void) +{ + // trivial example + int array[SIZE], n = 0; + while(n < SIZE) array[n++] = rand() % 2; + puts("Array filled!"); + n = 0; + while(n < SIZE) printf("%d ", array[n++]); + printf("\n"); + + // classic strcpy() implementation + // (copies a null-terminated string from src to dst) + char src[] = "Hello, world", dst[sizeof src], *p = dst, *q = src; + while((*p++ = *q++)) // double parentheses (that are not strictly necessary) + // used to suppress warnings, ensuring that this is an + // assignment (as opposed to a comparison) by intention, + // whose result is used as a truth value + ; // null statement + puts(dst); +}</pre></div> <p>Output:</p> +<div class="text source-text"><pre data-language="c">Array filled! +1 0 1 1 1 1 0 0 +Hello, world</pre></div> </div> <h3 id="References"> References</h3> <ul> +<li> C17 standard (ISO/IEC 9899:2018): </li> +<ul><li> 6.8.5.1 The while statement (p: 109) </li></ul> +<li> C11 standard (ISO/IEC 9899:2011): </li> +<ul><li> 6.8.5.1 The while statement (p: 151) </li></ul> +<li> C99 standard (ISO/IEC 9899:1999): </li> +<ul><li> 6.8.5.1 The while statement (p: 136) </li></ul> +<li> C89/C90 standard (ISO/IEC 9899:1990): </li> +<ul><li> 3.6.5.1 The while statement </li></ul> +</ul> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/language/while" title="cpp/language/while">C++ documentation</a></span> for <span class=""><span><code>while</code> loop</span></span> </td> +</tr> </table> <div class="_attribution"> + <p class="_attribution-p"> + © cppreference.com<br>Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.<br> + <a href="https://en.cppreference.com/w/c/language/while" class="_attribution-link">https://en.cppreference.com/w/c/language/while</a> + </p> +</div> |