Conditions

If-else Statement

Executes a block of code when a condition is true.

if condition {
    // code runs if condition is true
} else if anotherCondition {
    // code runs if it gets here and anotherCondition is true
} else {
    // code runs if none of the above are true
}

• Go lets you declare a variable that only exists in the if and else blocks:

  s := "Hello"
  
  if n := len(s); n == 1 {
  	fmt.Println("n is:", n)
  } else if n >= 2 {
  	fmt.Println("n is:", n)
  } else {
  	fmt.Println("Empty string", n)
  }
  
  // n is: 5
  
  fmt.Println("n is:", n) // <-- compiler: undefined: n

Switch Statement

Executes the block for the matching case.

switch expression {
case value1:
    // code runs if expression == value1
case value2:
    // code runs if expression == value2
case value3, value4:
    // code runs if expression == value3 or value4
default:
    // code runs if expression does not match any case
}

Go auto break after each case implicitly, but the keyword can still be used.

• Using the fallthrough keyword overrides the implicit break behavior and continues execution into the next case:

  a := 2
  
  switch a {
  case 1:
      fmt.Println("One")
  case 2:
      fmt.Println("Two")
      fallthrough
  case 3:
      fmt.Println("Three")
  case 4:
      fmt.Println("Four")
  default:
      fmt.Println("None of above")
  }
  
  // Two
  // Three

• You can also declare a variable for case matching that only exists within the switch block:

  s := "hi"
  
  switch n := len(s); n {
  case 1:
  	fmt.Println("n is:", n)
  case 2:
  	fmt.Println("n is:", n)
  default:
  	fmt.Println("None of above", n)
  }
  
  // n is: 2
  
  fmt.Println("n is:", n) // <-- compiler: undefined: n

• Omitting the expression makes the switch statement act like an if-else statement:

  a := 3
  
  switch {
  case a == 1:
      fmt.Println("One")
  case a == 2:
      fmt.Println("Two")
  case a == 3 || a == 4:
      fmt.Println("Three or Four")
  default:
      fmt.Println("None of above")
  }
  
  // Three or Four