PHP conditional judgment and multiple branches

* 1. Single branch: if(){ }

* 2. Double branch: if(){ }else{ }

* 3. Multiple branches: if()elseif (){}elseif()

* 4. Ternary operator: condition? true : false

* 5.switch structure

//1.Single branch

$grade = 55;
if ($grade < 60){ //单分支
  echo &#39;<p style="color:red">很不幸,您得补考</p>&#39;;
}

//2.Double branch

$grade = 70;
if ($grade < 60){ //双分支
  echo &#39;<p style="color:red">很不幸,您得补考</p>&#39;;
} else {    //$grade >= 60
  echo &#39;<p style="color:green">恭喜,及格啦~~</p>&#39;;
}

//3.Multiple branches

if ($grade < 60){ //多分支
  echo &#39;<p style="color:red">很不幸,您得补考</p>&#39;;
} else if ($grade>=60 && $grade < 80 ) {
  echo &#39;<p>考得不错哦~~</p>&#39;;
} else if ($grade>=80 && $grade <= 100){
  echo &#39;<p>真TM的是个天才~~</p>&#39;;
}

//4: Ternary operation: abbreviation mode of double branch

$age = 20;
echo $age>=18 ? &#39;<p>已成年,可以浏览本站</p>&#39; : &#39;<p style="color:red">未成年,请自觉离开</p>&#39;;

//5:switch: conditional selection operation

$program = 'php';
$program = 'mysql';
$program = 'javascript';
switch (strtolower($program)) {
  case 'php':
    echo &#39;<p>PHP是全世界最好的编程语言~~</p>&#39;;
    break;
  case &#39;mysql&#39;:
    echo &#39;<p>MySQL是全球最流行的免费的关系型数据库管理系统~~</p>&#39;;
    break;
  case &#39;html&#39;:
    echo &#39;<p>html是Web开发中用来写网页结构的标记语言</p>&#39;;
    break;
  case &#39;css&#39;:
    echo &#39;<p>css是控制页面显示的样式表文件~~</p>&#39;;
    break;
  case &#39;javascript&#39;: //javascript与js走同一分支语句
  case &#39;js&#39;:
    echo &#39;<p>javascript是全世界最流行的客户端脚本语言~~</p>&#39;;
    break;
  default:
    echo &#39;<p>您关心的编程语言,我们后期会有教程上线,请关注哟~~</p>&#39;;
    break;
}