03-logical-operators.md

Lab: Logical Operators

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See also Logical Operators 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 a, b bool = true, false
           fmt.Println(a && b)
           fmt.Println(a || b)
   }

   • false
     true
   • false
     false
   • true
     true
   • true
     false

   Reveal

   false
   true

   && is the AND operator. || is the OR operator. As will be seen later, ! is the NOT operator.

   Refer logic truth table

   a	b	a AND b	a OR b	a XOR b	NOT a	NOT b
   false	false	false	false	false	true	true
   true	false	false	true	true	false	true
   false	true	false	true	true	true	false
   true	true	true	true	false	false	false

   It should be noted that Go does not provide a logical XOR (exclusive-OR) operator where many other languages do, however XOR for two bool variables can be expressed like this: (a != b).

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

   package main
   
   import "fmt"
   
   func main() {
           var a, b bool = false, false
           fmt.Println(a && b)
           fmt.Println(a || b)
   }

   • false
     true
   • false
     false
   • true
     true
   • true
     false

   Reveal

   false
   false

   Refer boolean truth table in the answer to Q1 above

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

   package main
   
   import "fmt"
   
   func main() {
           var a, b bool = false, true
           fmt.Println(!a)
           fmt.Println(b)
   }

   • false
     true
   • false
     false
   • true
     true
   • true
     false

   Reveal

   true
   true

   Refer boolean truth table in the answer to Q1 above

   In the first Println we have applied the logical NOT (!) operator to the value of a. NOT false = true.

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

   package main
   
   import "fmt"
   
   func main() {
           var a bool = false
           result := 10 > 50
           fmt.Println(!(a && result))
   }

   • false
   • error
   • 1
   • true

   Reveal

   true

   Refer boolean truth table in the answer to Q1 above

   Let's break it down:

   • result := 10 > 50. This creates result as a bool variable, holding the value of 10 > 50 which is false.
   • Next, the bracketed expression is evaluated (a && result). a is false, result is false therefore this evaluates to false.
   • Finally, NOT is applied to the result of the previous evaluation, therefore answer is true.
5. What would be the output for the following program:

   package main
   
   import "fmt"
   
   func main() {
           var a bool = true
           result := 10 > 50
           fmt.Println(!(a || result))
   }

   • false
   • error
   • 1
   • true

   Reveal

   true

   Refer boolean truth table in the answer to Q1 above

   Let's break it down:

   • result := 10 > 50. This creates result as a bool variable, holding the value of 10 > 50 which is false.
   • Next, the bracketed expression is evaluated (a || result). a is true, result is false therefore this evaluates to true.
   • Finally, NOT is applied to the result of the previous evaluation, therefore answer is false.