php if...else 和 switch

<?php 
/*
    if($num%2 == 0){
        echo "num是一个偶数";
    }
    else{
        echo"num是一个奇数";
    }


    $grade = 81;
    if($grade > 80){
        //满足条件$grade > 80
        echo "该成绩的等级为优";
    }elseif ($grade > 70) {
        //不满足条件$grade > 80,但满足条件$grade > 70
        echo "该成绩的等级为良";
    }elseif($grade > 60){
        //不满足条件$grade > 70,但满足$grade > 60
        echo "该成绩的等级为中";
    }else{
        //不满足条件$grade > 60
        echo "该成绩的等级为差";
    }

    $week = 5;
    if($week == 1){
        echo "星期一";
    }elseif($week == 2){
        echo "星期二";
    }elseif($week == 3){
        echo "星期三";
    }elseif($week == 4){
        echo "星期四";
    }elseif($week == 5){
        echo "星期五";
    }elseif($week == 6){
        echo "星期六";
    }elseif($week == 7){
        echo "星期日";
    }
*/

    $week=4;
    switch($week){
    case 1:
       echo "星期一";
       break;
    case 2:
       echo "星期二";
       break;
      case 3:
       echo "星期三";
       break; 
    case 4:
       echo "星期四";
       break;
    case 5:
       echo "星期五";
       break;
    case 6:
       echo "星期六";
       break;
    case 7:
       echo "星期日";
       break;
    default:
       echo "输入的数字不正确...";
       break;
    }

 ?>