Control Flow

if / else

Go's if statement doesn't need parentheses around the condition, but the braces are mandatory. A unique Go feature: you can include a short statement before the condition, commonly used for error checking.

package main

import "fmt"

func main() {
    age := 20

    // Basic if/else
    if age >= 18 {
        fmt.Println("Adult")
    } else if age >= 13 {
        fmt.Println("Teenager")
    } else {
        fmt.Println("Child")
    }

    // if with short statement (very common in Go)
    if num := 42; num%2 == 0 {
        fmt.Println(num, "is even")
    } // num is NOT accessible here - scoped to if block
}

Adult
42 is even

for — The Only Loop

Go has only one looping construct: for. But it covers all cases — traditional C-style, while-like, and infinite loops. No while or do-while keywords exist.

// C-style for loop
for i := 0; i < 5; i++ {
    fmt.Print(i, " ")
}
fmt.Println() // 0 1 2 3 4

// While-style (condition only)
n := 1
for n < 100 {
    n *= 2
}
fmt.Println(n) // 128

// Infinite loop (break to exit)
count := 0
for {
    count++
    if count > 3 {
        break
    }
}
fmt.Println("Count:", count) // 4

0 1 2 3 4
128
Count: 4

range — Iterating Over Collections

range iterates over slices, maps, strings, and channels. It returns both the index/key and value:

// Range over slice
fruits := []string{"apple", "banana", "cherry"}
for i, fruit := range fruits {
    fmt.Printf("%d: %s\n", i, fruit)
}

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

// Range over map
scores := map[string]int{"Alice": 95, "Bob": 87}
for name, score := range scores {
    fmt.Printf("%s: %d\n", name, score)
}

// Range over string (iterates runes, not bytes)
for i, ch := range "Go!" {
    fmt.Printf("%d: %c\n", i, ch)
}

switch

Go's switch is cleaner than C/Java: no break needed — cases don't fall through by default. Use fallthrough explicitly if you want it (rare).

day := "Tuesday"
switch day {
case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday":
    fmt.Println("Weekday")
case "Saturday", "Sunday":
    fmt.Println("Weekend")
default:
    fmt.Println("Unknown")
}

// Switch without a condition (clean if/else chain)
hour := 14
switch {
case hour < 12:
    fmt.Println("Morning")
case hour < 17:
    fmt.Println("Afternoon")
default:
    fmt.Println("Evening")
}

Weekday
Afternoon

Practice Exercises