Go (Golang) Basic - 'for' Loop

Doing Things Over and Over Again

In our last part, we taught our code how to make decisions using if and switch. Now, let's teach it how to perform tasks repeatedly without us having to copy and paste our code. This process is called looping.

Many programming languages have several types of loops (while, do-while, for, forEach). Go simplifies this dramatically.

In Go, there is only one loop: the for loop. But it's incredibly versatile and can handle every looping scenario you need. Let's explore its three main forms.

1. The Classic for Loop

This is the most traditional form of a for loop, and you'll recognize it if you've used languages like C++, Java, or JavaScript. It's perfect when you know exactly how many times you want to repeat an action.

It consists of three parts, separated by semicolons:

1. The init statement: i := 0 (Initializes a counter. Runs once at the very beginning).
2. The condition expression: i < 5 (Checked before every loop. If true, the loop continues).
3. The post statement: i++ (Runs at the end of every loop iteration, usually to increment the counter).

Analogy: An assembly line worker who has been told to assemble exactly 5 boxes.

Code Example

package main

import "fmt"

func main() {
    // This loop will run 5 times (for i = 0, 1, 2, 3, 4)
    for i := 0; i < 5; i++ {
        fmt.Println("Assembling box number:", i)
    }
}

2. The for Loop as a while Loop

What if you don't know how many times to loop, but you know the condition to stop? In other languages, you'd use a while loop. Go handles this with a simplified for loop.

You just provide the condition, and the loop will run as long as that condition is true.

Analogy: Running on a treadmill. You don't know how many steps you'll take, but you'll keep running until you've burned 100 calories. The condition is caloriesBurned < 100.

Code Example

package main

import "fmt"

func main() {
    // This loop acts like a 'while' loop
    // It will run as long as 'number' is less than or equal to 5
    number := 1

    for number <= 5 {
        fmt.Println("The number is:", number)
        number++ // Important: Update the variable to avoid an infinite loop!
    }
}

3. The for range Loop: Iterating Over Collections

This is the most idiomatic and powerful way to loop over collections like slices and maps. It's Go's version of a forEach loop.

Analogy: Going through your grocery bag and looking at each item one by one.

Code Example with a Slice

When used with a slice, for range gives you the index and the value of each element.

package main

import "fmt"

func main() {
    fruits := []string{"Apple", "Banana", "Cherry"}

    for index, fruit := range fruits {
        fmt.Printf("Fruit at index %d is %s\n", index, fruit)
    }

    // If you only need the value, you can ignore the index with an underscore (_)
    fmt.Println("\nJust the fruit names:")
    for _, fruit := range fruits {
        fmt.Println(fruit)
    }
}

Code Example with a Map

When used with a map, it gives you the key and the value of each pair.

package main

import "fmt"

func main() {
    userProfile := map[string]string{
        "name": "Budi",
        "city": "Jakarta",
    }

    for key, value := range userProfile {
        fmt.Printf("%s: %s\n", key, value)
    }
}

Conclusion

Even with just one loop keyword, Go provides all the power you need to handle any repetitive task. You've now learned the three essential patterns:

• The classic for loop for a fixed number of iterations.
• The conditional for loop that acts like a while loop.
• The for range loop for iterating over collections.

Mastering loops is a huge step in becoming a proficient programmer. In our next part, we'll learn how to organize our code into clean, reusable blocks called Functions. See you there!