diff options
Diffstat (limited to 'devdocs/c/language%2Fif.html')
| -rw-r--r-- | devdocs/c/language%2Fif.html | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/devdocs/c/language%2Fif.html b/devdocs/c/language%2Fif.html new file mode 100644 index 00000000..b273c4e8 --- /dev/null +++ b/devdocs/c/language%2Fif.html @@ -0,0 +1,65 @@ + <h1 id="firstHeading" class="firstHeading">if statement</h1> <p>Conditionally executes code.</p> +<p>Used where code needs to be executed only if some condition is true.</p> +<h3 id="Syntax"> Syntax</h3> <table class="t-sdsc-begin"> <tr class="t-sdsc"> <td> <span class="t-spar">attr-spec-seq</span><span class="t-mark">(optional)</span> <code>if (</code> <span class="t-spar">expression</span> <code>)</code> <span class="t-spar">statement-true</span> </td> <td> (1) </td> <td class="t-sdsc-nopad"> </td> +</tr> <tr class="t-sdsc"> <td> <span class="t-spar">attr-spec-seq</span><span class="t-mark">(optional)</span> <code>if (</code> <span class="t-spar">expression</span> <code>)</code> <span class="t-spar">statement-true</span> <code>else</code> <span class="t-spar">statement-false</span> </td> <td> (2) </td> <td class="t-sdsc-nopad"> </td> +</tr> +</table> <table class="t-par-begin"> <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 <code>if</code> statement </td> +</tr> <tr class="t-par"> <td> <span class="t-spar">expression</span> </td> <td> - </td> <td> an <a href="expressions" title="c/language/expressions">expression</a> of any scalar type </td> +</tr> <tr class="t-par"> <td> <span class="t-spar">statement-true</span> </td> <td> - </td> <td> any <a href="statements" title="c/language/statements">statement</a> (often a compound statement), which is executed if <span class="t-spar">expression</span> compares not equal to <code>0</code> </td> +</tr> <tr class="t-par"> <td> <span class="t-spar">statement-false</span> </td> <td> - </td> <td> any <a href="statements" title="c/language/statements">statement</a> (often a compound statement), which is executed if <span class="t-spar">expression</span> compares equal to <code>0</code> </td> +</tr> +</table> <h3 id="Explanation"> Explanation</h3> <p><span class="t-spar">expression</span> must be an expression of any <a href="type#Type_groups" title="c/language/type">scalar type</a>.</p> +<p>If <span class="t-spar">expression</span> compares not equal to the integer zero, <span class="t-spar">statement-true</span> is executed.</p> +<p>In the form <span class="t-v">(2)</span>, if <span class="t-spar">expression</span> compares equal to the integer zero, <span class="t-spar">statement_false</span> is executed.</p> +<table class="t-rev-begin"> <tr class="t-rev t-since-c99"> +<td> <p>As with all other selection and iteration statements, the entire if-statement has its own block scope:</p> +<div class="c source-c"><pre data-language="c">enum {a, b}; +int different(void) +{ + if (sizeof(enum {b, a}) != sizeof(int)) + return a; // a == 1 + return b; // b == 0 in C89, b == 1 in C99 +}</pre></div> </td> <td><span class="t-mark-rev t-since-c99">(since C99)</span></td> +</tr> </table> <h3 id="Notes"> Notes</h3> <p>The <code>else</code> is always associated with the closest preceding <code>if</code> (in other words, if <span class="t-spar">statement-true</span> is also an if statement, then that inner if statement must contain an <code>else</code> part as well):</p> +<div class="c source-c"><pre data-language="c">int j = 1; +if (i > 1) + if(j > 2) + printf("%d > 1 and %d > 2\n", i, j); + else // this else is part of if(j>2), not part of if(i>1) + printf("%d > 1 and %d <= 2\n", i, j);</pre></div> <p>If <span class="t-spar">statement-true</span> is entered through a <a href="goto" title="c/language/goto">goto</a>, <span class="t-spar">statement-false</span> is not executed.</p> +<h3 id="Keywords"> Keywords</h3> <p><a href="../keyword/if" title="c/keyword/if"><code>if</code></a>, <a href="../keyword/else" title="c/keyword/else"><code>else</code></a></p> +<h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include <stdio.h> + +int main(void) +{ + int i = 2; + if (i > 2) { + printf("first is true\n"); + } else { + printf("first is false\n"); + } + + i = 3; + if (i == 3) printf("i == 3\n"); + + if (i != 3) printf("i != 3 is true\n"); + else printf("i != 3 is false\n"); +}</pre></div> <p>Output:</p> +<div class="text source-text"><pre data-language="c">first is false +i == 3 +i != 3 is false</pre></div> </div> <h3 id="References"> References</h3> <ul> +<li> C17 standard (ISO/IEC 9899:2018): </li> +<ul><li> 6.8.4.1 The if statement (p: 108-109) </li></ul> +<li> C11 standard (ISO/IEC 9899:2011): </li> +<ul><li> 6.8.4.1 The if statement (p: 148-149) </li></ul> +<li> C99 standard (ISO/IEC 9899:1999): </li> +<ul><li> 6.8.4.1 The if statement (p: 133-134) </li></ul> +<li> C89/C90 standard (ISO/IEC 9899:1990): </li> +<ul><li> 3.6.4.1 The if 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/if" title="cpp/language/if">C++ documentation</a></span> for <span class=""><span><code>if</code> statement</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/if" class="_attribution-link">https://en.cppreference.com/w/c/language/if</a> + </p> +</div> |