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Learn Go: Variables and Types
Updating Variables

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

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`.

``````spinachPrice := 1.50

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

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.

### Instructions

1.

Create a variable called `taxCalculation`, make it an `float64`.

2.

Add the value of `coolSneakers` to `taxCalculation` using the `+=` operator.

3.

Add the value of `niceNecklace` to `taxCalculation` using the `+=` operator.

4.

Calculate New York City sales tax for your cool new sneakers and nice necklace by taking 8.875% as sales tax.

Use the `*=` operator to multiply `taxCalculation` by `.08875`.