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PHP Numbers
Mathematical Assignment Operators

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.

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