Go for Loop

Introduction

The for loop is the only loop construct in Go, but it is versatile enough to handle a wide range of looping scenarios. In this chapter, you will learn the syntax and usage of the for loop in Go, with examples to illustrate different types of loops.

Basic Syntax

Simple for Loop

A simple for loop consists of three components: initialization, condition, and post statement. The loop executes as long as the condition is true.

Syntax:

for initialization; condition; post {
    // code to execute
}

Example:

package main

import "fmt"

func main() {
    for i := 0; i < 5; i++ {
        fmt.Println(i) // Output: 0 1 2 3 4
    }
}

The for Loop with Only Condition

You can omit the initialization and post statements, creating a loop that behaves like a while loop in other languages.

Example:

package main

import "fmt"

func main() {
    i := 0
    for i < 5 {
        fmt.Println(i) // Output: 0 1 2 3 4
        i++
    }
}

Infinite Loop

You can create an infinite loop by omitting all three components of the for loop.

Example:

package main

import "fmt"

func main() {
    i := 0
    for {
        fmt.Println(i)
        i++
        if i == 5 {
            break // Breaks out of the loop when i is 5
        }
    }
}

for-range Loop

The for-range loop iterates over elements in a variety of data structures such as arrays, slices, maps, strings, and channels.

Array or Slice

Example:

package main

import "fmt"

func main() {
    arr := []int{1, 2, 3, 4, 5}
    for index, value := range arr {
        fmt.Println("Index:", index, "Value:", value)
    }
}

String

When iterating over a string, the for-range loop returns the index and the Unicode code point (rune) of each character.

Example:

package main

import "fmt"

func main() {
    str := "Hello"
    for index, char := range str {
        fmt.Printf("Index: %d, Char: %c\n", index, char)
    }
}

Map

Example:

package main

import "fmt"

func main() {
    myMap := map[string]int{"one": 1, "two": 2, "three": 3}
    for key, value := range myMap {
        fmt.Println("Key:", key, "Value:", value)
    }
}

Channel

Example:

package main

import "fmt"

func main() {
    ch := make(chan int, 5)
    ch <- 1
    ch <- 2
    ch <- 3
    close(ch)

    for value := range ch {
        fmt.Println("Value:", value)
    }
}

Nested for Loops

You can use nested for loops to iterate over multi-dimensional data structures.

Example:

package main

import "fmt"

func main() {
    matrix := [][]int{
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9},
    }

    for i := range matrix {
        for j := range matrix[i] {
            fmt.Print(matrix[i][j], " ")
        }
        fmt.Println()
    }
}

Using Break and Continue

Break

The break statement exits the nearest enclosing loop.

Example:

package main

import "fmt"

func main() {
    for i := 0; i < 10; i++ {
        if i == 5 {
            break // Exit the loop when i is 5
        }
        fmt.Println(i)
    }
}

Continue

The continue statement skips the remaining code in the current iteration and moves to the next iteration of the loop.

Example:

package main

import "fmt"

func main() {
    for i := 0; i < 10; i++ {
        if i%2 == 0 {
            continue // Skip the rest of the loop for even numbers
        }
        fmt.Println(i) // Output: 1 3 5 7 9
    }
}

Conclusion

The for loop in Go is a powerful and flexible tool for iterating over data. By understanding how to use simple for loops, for-range loops, nested loops, and the break and continue statements, you can effectively control the flow of your program and perform complex iterations. The for loop is the cornerstone of repetition in Go, making it an essential concept to master.