Control Flow

package main

import "fmt"

func main() {
    // if/else — no parentheses around condition
    x := 42
    if x > 100 {
        fmt.Println("large")
    } else if x > 10 {
        fmt.Println("medium")
    } else {
        fmt.Println("small")
    }

    // if with initialization statement
    if n := computeSomething(); n > 0 {
        fmt.Println("positive:", n)
    } else {
        fmt.Println("non-positive:", n)
    }

    // switch — no fallthrough by default (unlike C)
    day := "Monday"
    switch day {
    case "Saturday", "Sunday":
        fmt.Println("weekend")
    case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday":
        fmt.Println("weekday")
    default:
        fmt.Println("unknown")
    }

    // switch with no condition (like if/else chain)
    n := 7
    switch {
    case n < 0:
        fmt.Println("negative")
    case n == 0:
        fmt.Println("zero")
    default:
        fmt.Println("positive")
    }
}

func computeSomething() int { return 42 }

package main

import "fmt"

func main() {
    // Classic for loop
    for i := 0; i < 5; i++ {
        fmt.Println(i)
    }

    // for as while
    n := 0
    for n < 10 {
        n += 3
    }
    fmt.Println(n)   // 12

    // Infinite loop
    // for {
    //     // break out when ready
    //     break
    // }

    // for range — iterate over slices, maps, strings
    fruits := []string{"apple", "banana", "cherry"}
    for i, v := range fruits {
        fmt.Printf("%d: %s\n", i, v)
    }

    // Ignore index with _
    for _, fruit := range fruits {
        fmt.Println(fruit)
    }

    // Range over a map
    capitals := map[string]string{
        "France": "Paris",
        "Japan":  "Tokyo",
        "UK":     "London",
    }
    for country, capital := range capitals {
        fmt.Printf("%s -> %s\n", country, capital)
    }

    // Range over a string (yields runes)
    for i, r := range "Hello" {
        fmt.Printf("%d: %c\n", i, r)
    }
}