ch03-flow-control.md

Controlling Conditional follow

Conditional flow in Go is achieved using if-else-if and switch-case.

If-Else-If

Format:

if <assignment or initialization>; <condition> {
      <things to do>
} else {

}

Just like in above example we can do multiple assignments in a single line and can base our condition on that.

Example:

if totalBytes, error := fmt.Printf("Hello, World!"); error != nil {
      os.Exit(1)
} else {
      fmt.Printf("%d", totalBytes)
}

Note that the <assignment or initialization> part is totally optional and is available if required. Also, if using <assignment or initialization> make sure to end it with a semi-colon( ; ).

Similarly, we can use multiple if statements in conjunction with else to form multiple condition sequence. e.g:

if totalBytes, error := fmt.Printf("Hello, World!"); error != nil {
      os.Exit(1)
} else if totalBytes == 0 {
      fmt.Printf("Empty string")
} else {
      fmt.Printf("%d", totalBytes)
}

Switch-Case

switch-case works a bit different in Go as compared to other languages such as C, for example, it doesn't fallthrough i.e, not all of the case defined will be evaluated as it is done in C. We can use the keyword fallthrough to explicitly enforce this behavior.

Format:

switch <variable> {
      case <condition>:
            <things to do>
      default:
            <things to do>
}

Note: The <variable> part with switch is totally optional.

Example:

message := "the quick brown fox jumps over the lazy dog"

vowel := 0
consonants := 0

for _, letter := range message{
      switch letter {
            case 'a', 'e', 'i', 'o', 'u':
                  vowel += 1
            default:
                  consonants += 1
      }
}

fmt.Printf("Vowels = %d, Consonants = %d", vowel, consonants)

Example, fallthrough:

message := "the quick brown fox jumps over the lazy dog"

vowel := 0
consonants := 0
aes := 0
zeds := 0

for _, letter := range message{
      switch letter {
            case 'a', 'e', 'i', 'o', 'u':
                  vowel += 1
                  fallthrough // Next case will also be evaluated.
            case 'a':
                  aes += 1
            case 'z':
                  zeds += 1
                  fallthrough // Next case will also be evaluated.
            default:
                  consonants += 1
      }
}

fmt.Printf("Vowels = %d, Consonants = %d, Aes = %d, Zeds = %d", vowel, consonants, aes, zeds)

Similarly, we could also do the following:

totalBytes, err := fmt.Printf("Hello, World!")

switch {
      case err != nil:
            os.Exit(1)
      case totalBytes == 0:
            fmt.Printf("Empty string")
      default:
            fmt.Printf("This is strange.")
}

Loops

Go has only one keyword to be used for loops i.e for but it supports all different kind of formats. Therefore we can use for to achieve the functionality of while and traditional C for.

while Format:

var counter bool
for !counter {
      <do-something>
      if <condition> {
            counter = true
      }
}

for Format:

for i := 0; i < 10; i++ { // we can also do double initialization and assignment i.e 'i, j := 1; i < 10; i, j = i++, j*2'
      <do-something>
}