php如何实现简单的算术运算？

<?php
  $a = 10;  //将整数10赋值给变量$a
  $b = 3.14;  //将浮点数3.14赋值给变量$b
  $c = "hello world"; //将字符串"hello world"赋值给变量$c
?>

<?php
  $a = 10;
  $b = 20;
  $c = $a + $b;
  echo $c;  //输出30
?>

<?php
  $a = 20;
  $b = 10;
  $c = $a - $b;
  echo $c;  //输出10
?>

<?php
  $a = 10;
  $b = 20;
  $c = $a * $b;
  echo $c;  //输出200
?>

<?php
  $a = 20;
  $b = 10;
  $c = $a / $b;
  echo $c;  //输出2
?>

<?php
  $a = 20;
  $b = 10;
  $c = $a % $b;
  echo $c;  //输出0
?>

<?php
  $a = 2;
  $b = 3;
  $c = $a ** $b;
  echo $c;  //输出8
?>

<?php
  $a = 10;
  $a++;
  echo $a;  //输出11
?>

<?php
  $a = 10;
  $a--;
  echo $a;  //输出9
?>

<?php
  $a = -10;
  $b = abs($a);
  echo $b;  //输出10
?>

<?php
  $a = 16;
  $b = sqrt($a);
  echo $b;  //输出4
?>

<?php
  $a = 30;
  $b = sin($a * pi() / 180);  //将角度转换为弧度
  echo $b;  //输出0.5
?>

<?php
  $a = 60;
  $b = cos($a * pi() / 180);  //将角度转换为弧度
  echo $b;  //输出0.5
?>

<?php
  $a = 45;
  $b = tan($a * pi() / 180);  //将角度转换为弧度
  echo $b;  //输出1
?>