PHP正在进行时-变量详解及字符串动态插入变量

<?php
  #合法的声明变量
  $_name;
  $account;
  $show_title;
  #赋值
  $color="red";
  #引用赋值
  $user_color=&$color;
?>

<?php
  $x=5;
  function show_x() {
    $x=3;
    echo $x;
  }
  show_x();
  echo $x;
?>

<?php
  $cost_fish=20.10;
  $cost_apple=2.45;
  #引用参数前面需要加上&符号
  function rise($cost_fish,&$cost_apple) {
    $cost_fish++;
    $cost_apple++;
  }
  rise($cost_fish,$cost_apple);
  echo $cost_fish."值传递参数<--->引用传递参数".$cost_apple;
?>

<?php
  $x=5;
  function show_x() {
    global $x;
    $x++;
  }
  show_x();
?>

<?php
  $x=5;
  function show_x() {
    global $x;
    $x++;
  }
  show_x();
?>

<?php
  function spend() {
    static $date=0;
    $date++;
    echo $date;
  }
  spend();
  spend();
?>

  //打印出$_SERVER 预定义的变量信息
  foreach($_SERVER as $var =>$value){
    echo "$var=>$value<br/>";
  }

  echo "张三李四王五叫上赵六一起去'喝酒'".

<?php
  $name="赵六";
  echo "张三李四王五\n叫上$name一起去\'喝酒\'.";
  echo "</br>";
  echo "张三李四王五\n叫上\$name一起去\'喝酒\'.";
  echo "</br>";
  echo "张三李四王五\n叫上{$name}一起去'喝酒'.";
  echo "</br>";
  echo '张三李四王五\n叫上$name一起去\'喝酒\'.';
  echo "</br>";
  echo '张三李四王五\n叫上{$name}一起去\'喝酒\'.';
  echo "</br>";
?>