Sometimes the value of our variables need to be adjusted. We know that we can update our variables using arithmetic operators like this:

var age = 99
age = age + 1
print(age)  // Prints 100

We also have the option of using compound assignment operators, a shorthand method for modifying the value of variables.

If we wanted to rewrite our previous code using a compound assignment operator (+=), our syntax would look like this:

var age = 99
age += 1
print(age)  // Prints 100

Notice that by using a compound assignment operator, we no longer need to reference age twice!

Here are some different compound assignment operators we can use:

• += add and assign the sum.
• -= subtract and assign the difference.
• *= multiply and assign the product.
• /= divide and assign the quotient.
• %= divide and assign the remainder.

Check out these operators in action as we modify the value of dollars five times using compound assignment operators:

var dollars = 5
dollars += 4   // same as dollars = 5 + 4
print(dollars) // Prints: 9

dollars -= 3   // same as dollars = 9 - 3
print(dollars) // Prints: 6

dollars *= 5   // same as dollars = 6 * 5
print(dollars) // Prints: 30

dollars /= 6   // same as dollars = 30 / 6
print(dollars) // Prints: 5

dollars %= 2   // same as dollars = 5 % 2
print(dollars) // Prints: 1

While the value of dollars started out as 5, the value changed every time we used a compound assignment operator; by the end of the program, dollars had a value of 1.

When using compound assignment operators, be sure to include a space before and after the assignment operator =; otherwise, we will receive an error.