PHP简单计算器
这个是运用PHP的条件控制语句写的，比较简单，消化下...
<html><head><title>PHP实现简单计算器（使用分支结构）</title></head><body><?php$mess = "";if( isset( $_POST["sub"])){if( $_POST["num1"] == ""){$mess .= "第一个数不能为空！<br>";}else if( !is_numeric($_POST["num1"])){$mess .= "第一个数必须为数字！<br>";}if( $_POST["num2"] == ""){$mess .= "第二个数不能为空！<br>";}else{if( !is_numeric($_POST["num2"])){$mess .= "第二个数必须为数字！<br>";}else if( $_POST["opt"] == "/" && $_POST["num2"] == 0){$mess .= "除数不能为0";}}}?><table border="1" align="center" width="400"><form action="" method="post"><caption><h1>计算器</h1></caption><tr><td><input type="text" size="4" name="num1" value="<?php echo $_POST["num1"] ?>" /></td><td><select name="opt"><option value="+"<?php echo $_POST["opt"] == "+" ? "selected" : "" ?>>+</option><option value="-"<?php echo $_POST["opt"] == "-" ? "selected" : "" ?>>-</option><option value="x"<?php echo $_POST["opt"] == "x" ? "selected" : "" ?>>x</option><option value="/"<?php echo $_POST["opt"] == "-" ? "selected" : "" ?>>/</option><option value="%"<?php echo $_POST["opt"] == "%" ? "selected" : "" ?>>%</option></select></td><td><input type="text" size="4" name="num2" value="<?php echo $_POST["num2"] ?>" /></td><td><input type="submit" name="sub" value="计算" /></td></tr></form><?phpif(isset($_POST["sub"])){echo '<tr><td colspan="4">';if( !$mess){$sum = 0;switch($_POST["opt"]){case "+":$sum = $_POST["num1"] + $_POST["num2"];break;case "-":$sum = $_POST["num1"] - $_POST["num2"];break;case "x":$sum = $_POST["num1"] * $_POST["num2"];break;case "/":$sum = $_POST["num1"] / $_POST["num2"];break;case "%":$sum = $_POST["num1"] % $_POST["num2"];break;}echo "结果: {$_POST['num1']} {$_POST['opt']} {$_POST['num2']} = {$sum}"; }else{echo $mess;}echo '</td></tr>';}?></table></body></html>