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                # 第一課 流程控制和運算 > 流程控制,break終止 continue 跳過 ``` <pre class="calibre14">``` <span class="token5">if</span><span class="token2">(</span>expr<span class="token2">)</span><span class="token2">{</span> <span class="token2">}</span><span class="token1">elseif</span><span class="token2">(</span>expr<span class="token2">)</span><span class="token2">{</span> <span class="token2">}</span><span class="token5">else</span><span class="token2">{</span> <span class="token2">}</span> <span class="token1">switch</span><span class="token2">(</span>val<span class="token2">)</span><span class="token2">{</span> case v1<span class="token2">:</span> <span class="token5">break</span><span class="token2">;</span> default<span class="token2">:</span> <span class="token2">}</span> <span class="token5">while</span><span class="token2">(</span>expr<span class="token2">)</span><span class="token2">{</span> <span class="token2">}</span> <span class="token5">do</span><span class="token2">{</span> <span class="token2">}</span><span class="token5">while</span><span class="token2">(</span>expr<span class="token2">)</span> <span class="token5">for</span><span class="token2">(</span>expr1<span class="token2">;</span>expr2<span class="token2">;</span>expr3<span class="token2">)</span><span class="token2">{</span> <span class="token2">}</span> <span class="token1">foreach</span><span class="token2">(</span>$arr as $k<span class="token">=</span><span class="token">></span>$v<span class="token2">)</span><span class="token2">{</span> <span class="token2">}</span> ``` ``` > 特殊寫法 endif endfor endwhile endswitch endforeach > 邏輯運算 || 或 && 與 ! 非 > 引用全局變量 ``` <pre class="calibre14">``` global $str<span class="token2">;</span> ``` ``` > 字符串定義 ``` <pre class="calibre14">``` $is <span class="token">=</span> <span class="token4">"ok"</span><span class="token2">;</span> $str <span class="token">=</span> <span class="token"><</span><span class="token"><</span><span class="token"><</span>EOF my name $is Jiang Qihui<span class="token">!</span> EOF<span class="token2">;</span> ``` ``` > 傳值和傳引用 ``` <pre class="calibre14">``` 按值傳遞:函數范圍內對值的任何改變在函數外部都會被忽略 按引用傳遞:函數范圍內對值的任何改變在函數外部也能反映出這些修改 優缺點:按值傳遞時,php必須復制值。特別是對于大型的字符串和對象來說,這將會是一個代價很大的操作。按引用傳遞則不需要復制值,對于性能提高很有好處。 ``` ``` > 控制錯誤@ ``` <pre class="calibre14">``` @<span class="token1">fn</span><span class="token2">(</span><span class="token2">)</span> ``` ``` > GET和POST區別 ``` <pre class="calibre14">``` get是發送請求HTTP協議通過url參數傳遞進行接收<span class="token2">,</span>而post是實體數據<span class="token2">,</span>可以通過表單提交大量信息<span class="token2">.</span> ``` ``` > session和cookie區別 ``` <pre class="calibre14">``` session<span class="token2">:</span>儲存用戶訪問的全局唯一變量<span class="token2">,</span>存儲在服務器上的php指定的目錄中的(session_dir)的位置進行的存放 cookie<span class="token2">:</span>用來存儲連續訪問一個頁面時所使用,是存儲在客戶端,對于Cookie來說是存儲在用戶WIN的Temp目錄中的。 兩者都可通過時間來設置時間長短 ``` ``` > echo(),print(),print\_r()區別 ``` <pre class="calibre14">``` echo是PHP語句<span class="token2">,</span> print和print_r是函數<span class="token2">,</span>語句沒有返回值<span class="token2">,</span>函數可以有返回值 <span class="token1">print</span><span class="token2">(</span><span class="token2">)</span>只能打印出簡單類型變量的值<span class="token2">(</span>如int<span class="token2">,</span>string<span class="token2">)</span> <span class="token1">print_r</span><span class="token2">(</span><span class="token2">)</span>可以打印出復雜類型變量的值<span class="token2">(</span>如數組<span class="token2">,</span>對象<span class="token2">)</span> echo 輸出一個或者多個字符串 ``` ``` > 優化mysql ``` <pre class="calibre14">``` 選擇正確數據類型<span class="token2">,</span>設置合適的字段長度 優化查詢語句<span class="token2">,</span>事務處理<span class="token2">,</span>建立索引 使用左右連接替代子查詢 ``` ``` > include和require,include\_once和require\_once ``` <pre class="calibre14">``` require 出現錯誤停止運行 include 出現錯誤繼續運行 include_once和require_once 有重復不會出錯<span class="token2">,</span>只處理一次 一般選用 require_once ``` ``` > 常見狀態 ``` <pre class="calibre16">``` <span class="token3">200</span> 成功 <span class="token3">404</span>未找到 <span class="token3">301</span>跳轉 <span class="token3">401</span>未授權 ``` ```
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