多分支结构与switch，循环方式遍历数组,while,for-php14章7.6

一.多分支结构与switch

1. 单分支模板语法,用:开头，关键字结束

   $amount = 1000;
   $payment = $amount;
   if ($amount >= 500) :
    $payment = $amount * 0.9;
   endif;
   echo '实际支付：', $payment, '<br>';

2. 双分支:if,else,endif

   $amount = 400;
   if ($amount >= 500) :
    $payment = $amount * 0.9;
   else :
    $payment = $amount;
   endif;
   echo '实际支付：', $payment, '<br>';

3. 多分支:if,elseif,else,endif

   $amount = 3000;
   if ($amount >= 1000 && $amount < 1500) :
    $payment = $amount * 0.9;
   elseif ($amount >= 1500 && $amount < 2000) :
    $payment = $amount * 0.8;
   elseif ($amount >= 2500) :
    $payment = $amount * 0.7;
   else :
    $payment = $amount;
   endif;
   echo '实际支付：', $payment, '<br>';

4. switch用来简化分支:switch,case,break,default

   $amount = 500;
   switch (true) {
    case $amount >= 1000 && $amount < 1500:
        $payment = $amount * 0.9;
        break;
    case $amount >= 1500 && $amount < 2000:
        $payment = $amount * 0.8;
        break;
    case $amount >= 2500:
        $payment = $amount * 0.7;
        break;
    default:
        $payment = $amount;
   }
   echo '实际支付：', $payment, '<br>';

• 4.2.switch通常用在单值判断中

  $discount = 0.8;
  $amount = 3300;
  switch ($discount):
    case 0.7:
        $payment = $amount * 0.7;
        break;
    case 0.8:
        $payment = $amount * 0.8;
        break;
    case 0.9:
        $payment = $amount * 0.9;
        break;
    default:
        $payment = $amount;
  endswitch;
  echo '实际支付：', $payment, '<br>';

  二.多种循环方式来遍历数组,while,for

  1.while条件判断型循环，入口判断
• 条件是真就执行循环

  $cities = ['北京', '深圳', '广州', '天津', '上海'];
  while ($city = current($cities)) {
    echo $city, '<br>';
    next($cities);
  }

• 怎么才能再次循环，必须指针复位

  reset($cities);
  while ($city = current($cities)) :
    echo $city, '<br>';
    next($cities);
  endwhile;

  2.判断型循环，出口判断型 do (…) while(条件)

• do - while 没有模板语法，此时第一个北京不见了

  do {
    echo $city, '<br>';
    next($cities);
  } while ($city = current($cities));

  3.计数型循环：for(循环变量初始化，循环条件，更新循环条件){…}

for ($i = 0; $i < count($cities); $i++) {
    echo $cities[$i], '<br>';
}
echo '<hr>';
for ($i = 0; $i < count($cities); $i++) :
    echo $cities[$i], '<br>';
endfor;

• 如果把第三个广州不要，广州值是2,输出拦截，后面的就终止不输出了

  for ($i = 0; $i < count($cities); $i++) :
    if ($i > 1) break;
    echo $cities[$i], '<br>';
  endfor;

• 选择性输出，跳过一些值广州

  for ($i = 0; $i < count($cities); $i++) :
    if ($i === 2) continue;
    echo $cities[$i], '<br>';
  endfor;