流程控制結構

• 循序：由上而下
• 選擇：條件判斷
• 重複：迴圈控制

if：單一條件判斷

範例：體重60，理想體重50，當體重大於理想體重印出You should go on a diet !

<?php 
    $weight = 60;
    $ideal_weight = 50;
    if($weight > $ideal_weight){
        echo "You should go on a diet !";
    }  
?>

輸出：
You should go on a diet !

if-else：二選一條件

範例：體重40，理想體重50，當體重大於理想體重印出You should go on a diet !否則印出You should eat more !

<?php 
    $weight = 40;
    $ideal_weight = 50;
    if($weight > $ideal_weight){
        echo "You should go on a diet !";
    }else{
        echo "You should eat more!";
    }
?>

輸出：
You should eat more!

if-elseif：多個選擇

範例：BMI檢測，大於24印出Overweight ! ，小於18.5印出Too Skin !，介於之間印出Ideal Weight ! 當BMI=25時。

<?php 
    $bmi = 25;
    $bmi_min = 18.5;
    $bmi_max = 24;
    if($bmi>$bmi_max){
        echo "Overweight!";
    }elseif($bmi>=$bmi_min && $bmi<=$bmi_max){
        echo "Ideal Weight!";
    }elseif($bmi<$bmi_min){
        echo "Too Skin!";
    }
?>

輸出：
Overweight!

switch：多個選擇

範例：依照數字印出所對應的星期英文字，當$day=2時。記得在後方加入break;才能跳出不繼續執行程式。

<?php 
   $day = 2;
   switch($day){
       case 1:
        echo "Monday";
        break;
       case 2:
        echo "Tuesday";
        break;
       case 3:
        echo "Wednesday";
        break;
       case 4:
        echo "Thursday";
        break;
       case 5:
        echo "Friday";
        break;
       case 6:
        echo "Saturday";
        break;
       case 7:
        echo "Sunday";
        break;
   }
?>

輸出：
Tuesday