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 (expr)
    statement

<?php
$i = 1;
while ($i <= 10) {
    echo $i++; 
}

$i = 1;
while ($i <= 10):
    print $i;
    $i++;
endwhile;
?>

do {
  要执行的代码;
} while (条件为真);

<?php
$i = 0;
do {
   echo $i;
} while ($i > 0);
?>

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

$i = 0;
while (++$i) {
    switch ($i) {
    case 5:
        echo "At 5<br />\n";
        break 1;  /* 只退出 switch. */
    case 10:
        echo "At 10; quitting<br />\n";
        break 2;  /* 退出 switch 和 while 循环 */
    default:
        break;
    }
}

$i = 0;
while ($i++ < 5) {
    echo "Outer<br />\n";
    while (1) {
        echo "Middle<br />\n";
        while (1) {
            echo "Inner<br />\n";
            continue 3;
        }
        echo "This never gets output.<br />\n";
    }
    echo "Neither does this.<br />\n";
}

<?php
goto a;
echo 'Foo';
 
a:
//'Bar'
echo 'Bar';
?>