前端学PHP之语句

if (条件) {
  当条件为 true 时执行的代码;
}

if (条件) {
  条件为 true 时执行的代码;
} else {
  条件为 false 时执行的代码;
}

if (条件) {
  条件为 true 时执行的代码;
} elseif (条件) {
  条件为 true 时执行的代码;
} else {
  条件为 false 时执行的代码;
}

<?php
$t=date("H");
if ($t<"10") {
  echo "Have a good morning!";
} elseif ($t<"20") {
  echo "Have a good day!";
} else {
  echo "Have a good night!";
}
?>

switch (expression)
{
case label1:
  code to be executed if expression = label1;
  break;  
case label2:
  code to be executed if expression = label2;
  break;
default:
  code to be executed
  if expression is different 
  from both label1 and label2;
}

<?php
switch ($x)
{
case 1:
  echo "Number 1";
  break;
case 2:
  echo "Number 2";
  break;
case 3:
  echo "Number 3";
  break;
default:
  echo "No number between 1 and 3";
}
?>

while (条件为真) {
  要执行的代码;
}

<?php
$sum = 12;//小宠物当前的饥饿程度
echo "我饿啦:-(";
echo "<br />";
while($sum<100)
{//小宠物的饥饿程度到100，表示小宠物吃饱啦,不用继续喂了，没吃饱继续喂食
    $num = rand(1,20);//随机数，模拟喂食小宠物的小面包
  $sum = $sum + $num; //小宠物吃小面包
  echo "我还没吃饱呢！";
  echo "<br />";
}
echo "终于吃饱啦^_^";
?>

do {
  要执行的代码;
} while (条件为真);

<?php
  $sum  = 0; 
  do{
    $num = rand(1,6);//获取1至6的随机数，模拟掷骰子
    $sum = $sum  + $num;//前进步长
  }while($num==6);
  echo "do...while例子执行完毕，前进：".$sum ."<br />";
?>

for (init counter; test counter; increment counter) {
  code to be executed;
}    

<?php 
for ($x=0; $x<=10; $x++) {
  echo "数字是：$x <br>";
} 
?>

foreach ($array as $value) {
  code to be executed;
}    

<?php 
$colors = array("red","green","blue","yellow"); 
foreach ($colors as $value) {
  echo "$value <br>";
}
?>

foreach ($array as $index => $value) {
  code to be executed;
} 

<?php 
$colors = array(
  "r"=>"red",
  "g"=>"green",
  "b"=>"blue",
  "y"=>"yellow"); 
foreach ($colors as $key => $value) {
  echo $key.":".$value."<br>";
}
?>