Operator Precedence in Go

TL ; DR:

• When we string operations together, Go must know which one to do first. This is called operator precedence.

  
  

• *, /, and % are performed before + and -:

  fmt.Println(1 + 2 * 3)     // Prints 7
  fmt.Println(6 - 4 / 2)     // Prints 4
  fmt.Println(5 * 4 - 2 / 2) // Prints 19
  

  
  

• We can add () to force an operation to be performed first:

  fmt.Println((1 + 2) * 3)     // Prints 9
  fmt.Println((6 - 4) / 2)     // Prints 1
  fmt.Println(5 * (4 - 2) / 2) // Prints 5
  

Full lesson:

When we string operations together, Go must know which one to do first. This is called operator precedence.

This is the hierarchy from highest precedence to lowest precedence:

• Parentheses are always respected
• Multiplication, division, and remainder
• Addition and subtraction
• Left to right when operators have the same precedence

First example:

fmt.Println(1 + 2 * 3) // Output: 7

Multiplication is executed before addition, so:

1 + 2 * 3 = 1 + 6 = 7

Second example:

fmt.Println((1 + 2) * 3) // Output: 9

What's inside parentheses is executed before multiplication, so:

(1 + 2) * 3 = 3 * 3 = 9

Third example:

fmt.Println(6 / 4 * 3 + 5) // Output: 8

Multiplication and division come before addition. They have the same priority, so they are executed from left to right. Because these are integers, 6 / 4 evaluates to 1:

6 / 4 * 3 + 5 = 1 * 3 + 5 = 3 + 5 = 8

Fourth example:

fmt.Println(6 / ((4 + 2) / 3)) // Output: 3

Go sees parentheses, so it evaluates the inner expression first:

6 / ((4 + 2) / 3) = 6 / x, where x = (4 + 2) / 3

Compute x first:
(4 + 2) / 3 = 6 / 3 = 2

Then replace x with 2:
6 / ((4 + 2) / 3) = 6 / 2 = 3

Assignment
Follow the Coding Tutorial and let's practice with operator precedence!

Hint
Look at the examples above if you get stuck.