PHP 从入门到精通：数据类型、运算符与流程控制<\/h1>

0x01 PHP 数据类型<\/h2>

一、基础数据类型<\/h3>

整型 (int)<\/strong><\/p>

存储整数<\/li>
示例：$num = 123;<\/code><\/li> <\/ul> <\/li>
浮点型 (float)<\/strong><\/p> 存储小数或超出整型范围的数<\/li> 示例： $f1 =<\/span> 1.23<\/span>; <\/span><\/span>$f2 =<\/span> 1.23e10<\/span>; \/\/ 科学计数法 <\/span><\/span><\/span><\/span>$f3 =<\/span> PHP_INT_MAX<\/span> +<\/span> 1<\/span>; \/\/ 超出整型范围自动转为浮点型 <\/span><\/span><\/span><\/span>var_dump<\/span>($f1, $f2, $f3); <\/span><\/span><\/code><\/pre><\/li> <\/ul> <\/li> 字符串 (String)<\/strong><\/p> 用于存储文本数据<\/li> <\/ul> <\/li> 布尔类型 (Boolean)<\/strong><\/p> 只有两个值：true<\/code> 和 false<\/code><\/li> 主要用于条件判断<\/li> <\/ul> <\/li> <\/ol> 二、复杂数据类型<\/h3> 数组 (array)<\/strong><\/p> 存储多个值的集合<\/li> <\/ul> <\/li> 对象 (object)<\/strong><\/p> 面向对象编程的基础<\/li> <\/ul> <\/li> <\/ol> 三、特殊数据类型<\/h3> 资源类型 (Resource)<\/strong><\/p> 表示外部资源，如数据库连接、文件句柄等<\/li> <\/ul> <\/li> Null<\/strong><\/p> 表示变量没有值<\/li> <\/ul> <\/li> <\/ol> 0x02 PHP 运算符<\/h2> 原码、反码与补码<\/h3> 正数<\/strong><\/p> 原码、反码、补码都相同<\/li> <\/ul> <\/li> 负数<\/strong><\/p> 反码<\/strong>：符号位不变，其他位取反<\/li> 补码<\/strong>：反码 + 1<\/li> 示例： 5原码: 10000101 反码: 11111010 补码: 11111011 <\/code><\/pre> <\/li> <\/ul> <\/li> <\/ol> 位运算符<\/h3> 注意<\/strong>：<\/p> 系统进行位运算时都使用补码<\/li> 运算结束后必须转换回原码才是最终显示的数据<\/li> <\/ol> 位运算符<\/strong>：<\/p> &<\/code>：按位与 - 两个位都为1，结果为1，否则为0<\/li> |<\/code>：按位或 - 两个位有一个为1，结果为1<\/li> ~<\/code>：按位非 - 一个位为1则为0，为0则为1<\/li> ^<\/code>：按位异或 - 两个位相同为0，不同为1<\/li> <<<\/code>：按位左移 - 整个位向左移动一位，右边补0<\/li> >><\/code>：按位右移 - 整个位向右移动一位，左边补符号位（正数补0，负数补1）<\/li> <\/ul> 0x03 PHP 流程控制<\/h2> 控制结构分类<\/h3> 顺序结构<\/strong><\/p> 代码从上往下顺序执行<\/li> <\/ul> <\/li> 分支结构<\/strong><\/p> 根据条件执行不同的代码块<\/li> <\/ul> if 分支<\/strong>：<\/p> 最简if：<\/p> if<\/span> (条件表达式<\/span>) { <\/span><\/span> \/\/ 满足条件执行的代码 <\/span><\/span><\/span><\/span>} <\/span><\/span><\/code><\/pre>示例：<\/p> $day =<\/span> "sunday1"<\/span>; <\/span><\/span>if<\/span> ($day ==<\/span> "sunday"<\/span>) { <\/span><\/span> echo<\/span> 'go out'<\/span>; <\/span><\/span>} <\/span><\/span><\/code><\/pre><\/li> 基础if：<\/p> if<\/span> (条件表达式<\/span>) { <\/span><\/span> \/\/ 满足条件执行的代码 <\/span><\/span><\/span><\/span>} else<\/span> { <\/span><\/span> \/\/ 不满足条件执行的代码 <\/span><\/span><\/span><\/span>} <\/span><\/span><\/code><\/pre><\/li> 复杂if：<\/p> if<\/span> (条件表达式1<\/span>) { <\/span><\/span> \/\/ 代码块1 <\/span><\/span><\/span><\/span>} elseif<\/span> (条件表达式2<\/span>) { <\/span><\/span> \/\/ 代码块2 <\/span><\/span><\/span><\/span>} else<\/span> { <\/span><\/span> \/\/ 代码块3 <\/span><\/span><\/span><\/span>} <\/span><\/span><\/code><\/pre><\/li> <\/ul> switch 分支<\/strong>：<\/p> switch<\/span> (条件表达式<\/span>) { <\/span><\/span> case<\/span> 值1<\/span>:<\/span> <\/span><\/span> \/\/ 代码段1; <\/span><\/span><\/span><\/span> break<\/span>; <\/span><\/span> case<\/span> 值2<\/span>:<\/span> <\/span><\/span> \/\/ 代码段2; <\/span><\/span><\/span><\/span> break<\/span>; <\/span><\/span> default<\/span>:<\/span> <\/span><\/span> \/\/ 默认代码; <\/span><\/span><\/span><\/span> break<\/span>; <\/span><\/span>} <\/span><\/span><\/code><\/pre>示例：<\/p> $day =<\/span> 1<\/span>; <\/span><\/span>switch<\/span> ($day) { <\/span><\/span> case<\/span> 1<\/span>:<\/span> echo<\/span> '1'<\/span>; break<\/span>; <\/span><\/span> case<\/span> 2<\/span>:<\/span> echo<\/span> '2'<\/span>; break<\/span>; <\/span><\/span> case<\/span> 3<\/span>:<\/span> echo<\/span> '3'<\/span>; break<\/span>; <\/span><\/span> default<\/span>:<\/span> echo<\/span> 'error'<\/span>; break<\/span>; <\/span><\/span>} <\/span><\/span><\/code><\/pre><\/li> 循环结构<\/strong><\/p> 在条件控制范围内重复执行代码块<\/li> <\/ul> for 循环<\/strong>：<\/p> for<\/span> (初始化<\/span>; 条件判断<\/span>; 变量变化<\/span>) { <\/span><\/span> \/\/ 循环体 <\/span><\/span><\/span><\/span>} <\/span><\/span><\/code><\/pre>执行原理：<\/p> 执行初始化（1次）<\/li> 判断条件（N次）满足则执行循环体<\/li> 不满足则结束循环<\/li> <\/ul> <\/li> 执行循环体（N次）<\/li> 执行变量变化（N次）<\/li> 重复2-4步直到条件不满足<\/li> <\/ol> 特殊用法（死循环）：<\/p> for<\/span> (;;) { <\/span><\/span> echo<\/span> "hello world"<\/span>; <\/span><\/span>} <\/span><\/span><\/code><\/pre>while 循环<\/strong>：<\/p> while<\/span> (条件表达式<\/span>) { <\/span><\/span> \/\/ 循环体 <\/span><\/span><\/span><\/span> \/\/ 循环条件变化 <\/span><\/span><\/span><\/span>} <\/span><\/span><\/code><\/pre>示例：<\/p> $i =<\/span> 1<\/span>; <\/span><\/span>while<\/span> ($i <=<\/span> 10<\/span>) { <\/span><\/span> echo<\/span> $i, '<br>'<\/span>; <\/span><\/span> $i++<\/span>; <\/span><\/span>} <\/span><\/span><\/code><\/pre>do-while 循环<\/strong>：<\/p> do<\/span> { <\/span><\/span> \/\/ 循环体 <\/span><\/span><\/span><\/span> \/\/ 循环条件变化 <\/span><\/span><\/span><\/span>} while<\/span> (条件表达式<\/span>); <\/span><\/span><\/code><\/pre>示例：<\/p> $i =<\/span> 1<\/span>; <\/span><\/span>do<\/span> { <\/span><\/span> if<\/span> ($i %<\/span> 2<\/span> !=<\/span> 1<\/span>) { <\/span><\/span> echo<\/span> $i, '<br\/>'<\/span>; <\/span><\/span> } <\/span><\/span> $i++<\/span>; <\/span><\/span>} while<\/span> ($i <=<\/span> 10<\/span>); <\/span><\/span><\/code><\/pre>循环控制<\/strong>：<\/p> continue<\/code>：跳过当前循环剩余部分，进入下一次循环 continue n<\/code>：跳过n层循环<\/li> <\/ul> <\/li> break<\/code>：终止当前循环 break n<\/code>：终止n层循环<\/li> <\/ul> <\/li> <\/ul> 示例：<\/p> $i =<\/span> 1<\/span>; <\/span><\/span>while<\/span> ($i <=<\/span> 100<\/span>) { <\/span><\/span> if<\/span> ($i %<\/span> 5<\/span> !=<\/span> 0<\/span>) { <\/span><\/span> $i++<\/span>; <\/span><\/span> continue<\/span>; <\/span><\/span> } <\/span><\/span> echo<\/span> $i++<\/span>, '<br>'<\/span>; <\/span><\/span>} <\/span><\/span><\/code><\/pre>foreach 循环<\/strong>：<\/p> 专门用于遍历数组<\/li> <\/ul> <\/li> <\/ol> 流程控制替代语法<\/h3> 用于在HTML中嵌入PHP代码时提高可读性：<\/p> <?<\/span>php<\/span> for<\/span> ($i =<\/span> 1<\/span>; $i <<\/span> 10<\/span>; $i++<\/span>):<\/span> ?><\/span> <\/span><\/span><\/span> <tr> <\/span><\/span><\/span> <?php for ($j = 1; $j <= $i; $j++): ?> <\/span><\/span><\/span> <td><?php echo $i."*".$j.'='.$i*$j; ?><\/td> <\/span><\/span><\/span> <?php endfor; ?> <\/span><\/span><\/span> <\/tr> <\/span><\/span><\/span><?php endfor; ?> <\/span><\/span><\/span><\/code><\/pre>替代语法对应关系：<\/p> if<\/code>: if (条件): ... endif;<\/code><\/li> for<\/code>: for (;;): ... endfor;<\/code><\/li> while<\/code>: while (条件): ... endwhile;<\/code><\/li> foreach<\/code>: foreach (): ... endforeach;<\/code><\/li> <\/ul> 总结<\/h2> 本文详细介绍了PHP的三大基础概念：<\/p> 数据类型<\/strong>：包括基础类型、复杂类型和特殊类型<\/li> 运算符<\/strong>：重点讲解了位运算符及其底层原理<\/li> 流程控制<\/strong>：涵盖分支结构、循环结构及其控制语句<\/li> <\/ol> 掌握这些基础知识是学习PHP编程的重要基础，特别是流程控制部分在实际开发中应用非常广泛。<\/p>