How to Convert a Positive Number to Negative in PHP Using Multiplication

In PHP, you can turn a positive number into a negative one by multiplying it by -1.

There are two ways to perform this multiplication: using the * operator or the multiplication‑assignment operator *=.

Method 1 – using the * operator : multiply the variable by -1 directly.

<?php
header("Content-type:text/html;charset=utf-8");
$number = 99;
echo "原正数：" . $number . "<br>";
$number = $number * (-1);
echo "转换后的负数：" . $number; // 输出 -99
?>

Method 2 – using the *= operator : the operator performs the multiplication and assigns the result back to the variable.

<?php
header("Content-type:text/html;charset=utf-8");
$number = 88;
echo "原正数：" . $number . "<br>";
$number *= -1;
echo "转换后的负数：" . $number; // 输出 -88
?>