Variables are different from constants because we can update them. This update feature becomes incredibly important when we need to use the original value of a variable for a calculation (or any general manipulation) and then update the variable to store the newly calculated value. Let’s say we were keeping track the cost of items in our grocery basket:

var basketTotal float64
carrotPrice := 0.75

basketTotal = basketTotal + carrotPrice
fmt.Println(basketTotal) // Prints: 0.75

Notice that we used the original value of basketTotal which wasn’t assigned a value, so it has a default value of 0.0, added carrotPrice (0.75) and then assigned the computed value to basketTotal.

If we add another item:

spinachPrice := 1.50
basketTotal = spinachPrice + basketTotal
fmt.Println(basketTotal) // Prints: 2.25

This time, we added spinachPrice to basketTotal and stored the new value again in basketTotal, thereby updating our running total! Updating a variable by adding another number to itself and saving the new value is so common that Go has a shorthand for it, the += operator. We could have done the same operation using the following syntax:

spinachPrice := 1.50
basketTotal += spinachPrice
fmt.Println(basketTotal) // Prints: 2.25

Notice that basketTotal = spinachPrice + basketTotal and basketTotal += spinachPrice do the same thing! We can also do the same for strings (i.e. concatenating strings together):

command := "Hold my "
beverage := "soda"

command += beverage
fmt.Println(command) // Prints: Hold my soda

See how we were able to update command using += to store the value of both strings together?

In addition to += (yes, pun intended), Go has other arithmetic operations that perform calculations and update the variable’s value:

• -= to subtract from the variable.
• *= to multiply the variable by a factor.
• /= to divide the variable by a dividend.

Let’s get some practice using these shorthand operators.