PHP—函數二_學習筆記 php四捨五入函數 php延時函數 php排序函

1.變數函數（可變函數）
變數的值是一個函數的名稱。
e.g:

<code>```
<span><span>function</span><span>show</span><span>(<span>$a</span>,<span>$b</span>)</span>{</span><span>return</span><span>$a</span>+<span>$b</span>;
}
<span>$str</span>=<span>"show"</span>;
<span>echo</span><span>$str</span>(<span>10</span>,<span>5</span>);
``</code>

2.回呼函數
回調函數，函數的參數是另一個函數的名字。

<code>```
<span><span>function</span><span>show</span><span>(<span>$a</span>,<span>$b</span>)</span>{</span><span>return</span><span>$a</span>+<span>$b</span>;
}
<span><span>function</span><span>test</span><span>(<span>$i</span>,<span>$j</span>,<span>$k</span>)</span>{</span><span>return</span><span>$k</span>(<span>$i</span>,<span>$j</span>);
}
<span>$num</span>=test(<span>10</span>,<span>5</span>,<span>"show"</span>);
<span>echo</span><span>$num</span>;
``</code>

3.遞歸函數
一個函數在它的函式體內呼叫它本身稱為遞歸呼叫（函式內部自己呼叫自己）

<code><span><span>function</span><span>test</span><span>()</span>{</span><span>static</span><span>$num</span>;
       <span>$num</span>++;
       <span>if</span>(<span>$num</span><=<span>10</span>){
         <span>echo</span><span>'this is num '</span>.<span>$num</span>.<span>'<br>';
         test();<span>//自己再调用自己</span>
       }
    }

    test();</code>

4.function_exits(string $function_name)
判斷一下函數是否存在,回傳的是bool；

<code><span>if</span>(function_exists(<span>'show'</span>)){
        <span>exit</span>(<span>'此函数名称已存在'</span>);
    }<span>else</span>{
        <span><span>function</span><span>show</span><span>()</span>{</span>        }
    }

    var_dump(function_exists(<span>'show'</span>));</code>

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