04-assignment-operators.md

Lab: Assignment Operators

Take me to the lab!

Help for the VSCode editor.

See also Assignment in the Go manual.

All the code fragments in this lab are complete mini-programs, so you can paste them into the editor and run them to see the results:

Running the code fragments

1. Right click in Explorer pane to create a new file, e.g. test.go
2. Paste the question code snippet into the editor pane
3. Open the terminal window and execute go run test.go
4. Re-use your test.go file by replacing the content with that of the next question.

Questions

1. What would be the output for the following program:

   package main
   
   import "fmt"
   
   func main() {
           var x, y string = "foo", "bar"
           x += y
           fmt.Println(x)
   }

   • foobar
   • foo
   • error
   • bar

   Reveal

   foobar

   += is "add and assign", and is equivalent to x = x + y. When you add two strings, the result is the concatenation of the strings.

2. What would be the output for the following program:

   package main
   
   import "fmt"
   
   func main() {
           var x, y int = 27, 7
           x /= y
           fmt.Println(x)
   }

   • 6
   • 3
   • error
   • 6.00

   Reveal

   3

   /= is "divide and assign", and is equivalent to x = x / y. Since we have two integers, then an integer division is performed and the remainder is discarded: 27 / 7 = 3 r6

3. What would be the output for the following program:

   package main
   
   import "fmt"
   
   func main() {
           var x, y float64 = 27.9, 7.0
           x -= y
           fmt.Println(x)
           x += y
           fmt.Println(x)
   }

   • 27.9
     20.9
   • 20.9
     27.9
   • 20.9
     7.9
   • 27.9
     9.0

   Reveal

   20.9
   27.9

   • x -= y ... x = 27.9 - 7.0 = 20.9, then
   • x += y ... x = 20.9 + 7.0 = 27.9
4. What would be the output for the following program:

   package main
   
   import "fmt"
   
   func main() {
           var x, y int = 100,9
           x /= y
           fmt.Println(x)
           x %= y
           fmt.Println(x)
   }

   • 2
     2
   • 11
     2
   • 2
     11
   • 11
     11

   Reveal

   11
   2

   • x /= y ... x = 100 / 9 = 11. Remember this is an integer division so the remainder is discarded, then
   • x %= y ... x = 11 % 9 = 2. x is now 11 from the previous division assignment. Remainder of 11 divided by 2 is 2.
5. Which of these operator assigns the remainder of the division x

   • /=
   • *=
   • %=
   • \=

   Reveal

   %=

   This is the modulo (remainder) assignment operator.

   • /= is divide assign
   • *= is multiply assign
   • \= is a syntax error and won't compile.