One common task when manipulating number variables is to reassign them to their old value with some operation performed on it.

$savings = 800; $bike_cost = 75; $savings = $savings - $bike_cost; echo $savings; // Prints: 725

This is such a common task that PHP provides a shorter syntax using arithmetic assignment operators:

Operation: |
Long Syntax: |
Short Syntax: |
---|---|---|

Add | $x = $x + $y | $x += $y |

Subtract | $x = $x - $y | $x -= $y |

Multiply | $x = $x * $y | $x *= $y |

Divide | $x = $x / $y | $x /= $y |

Mod | $x = $x % $y | $x %= $y |

We could use this shorter syntax to rewrite the above code:

$savings = 800; $bike_cost = 75; $savings -= $bike_cost; echo $savings; // Prints: 725

With mathematical assignment operators, PHP doesn’t allow spaces between the two characters.

Ready for one more shortcut? Increment operators allow us to subtract or add one to a number with just two characters.

$age = 89; $age++; echo $age; // Prints: 90 $days_til_vacation = 7; $days_til_vacation--; echo $days_til_vacation; // Prints: 6

In the code above, we used the post-increment (`++`

) operator to add one to `$age`

and we used the post-decrement operator (`--`

) to subtract one from `$days_til_vacation`

.

Those keystrokes can add up, so let’s practice using arithmetic assignment operators on variables!

### Instructions

**1.**

We’re going to do a mathematical “magic” trick. Create a variable, `$my_num`

and assign as its value any number.

Next, create a second variable, `$answer`

and assign `$my_num`

as its value.

**2.**

Use the addition assignment operator to add 2 to `$answer`

.

**3.**

Use the multiplication assignment operator to multiply `$answer`

by 2.

**4.**

Use the subtraction assignment operator to subtract 2 from `$answer`

.

**5.**

Use the division assignment operator to divide `$answer`

by 2.

**6.**

Almost there. Use the subtraction assignment operator to subtract your original number (`$my_num`

) from `$answer`

. Finally, use `echo`

to print `$answer`

to the terminal.

If everything went as it should, `$answer`

should be 1. No matter what your original number was! Don’t believe us? Go ahead try it with a different number for the value of `$my_num`

.