Go by Example: For

Welcome to another installment of our Go by Example series! In this article, we'll be diving into the usage and syntax of the for loop in Go. The for loop is one of the fundamental control flow constructs in any programming language, and Go provides a versatile and concise way to use it. Let's get started!

The Basics

The basic syntax for a for loop in Go looks like this:

for initialisation; condition; post {
    // Code to be executed
}

Let's break down each component of the for loop:

• Initialisation: This is an optional statement that is executed before the loop starts. It typically initializes the loop counter or any other variables needed for the loop.
• Condition: The loop continues to execute as long as this condition is true. If the condition evaluates to false, the loop exits.
• Post: This statement is executed at the end of each iteration of the loop. It typically increments the loop counter or updates any other variables as needed.

Let's look at a simple example:

for i := 0; i < 5; i++ {
    fmt.Println(i)
}

In this example, the loop will print the values 0 to 4. Let's break down the code:

• i := 0 is the initialization statement. It declares a variable i and initializes it to 0.
• i < 5 is the condition. As long as i is less than 5, the loop will continue to execute.
• i++ is the post statement. It increments i by 1 at the end of each iteration.
• fmt.Println(i) is the code to be executed. It prints the value of i at each iteration.

The output of this code will be:

0
1
2
3
4

Infinite Loops

Go also allows you to create infinite loops using the for loop construct when you omit the condition. For example:

for {
    // Code to be executed
}

In this case, the code inside the loop will continue to execute indefinitely until you explicitly break out of the loop using the break statement.

For Each Loop

Go does not have a built-in for each loop like some other languages. However, you can achieve similar functionality using the range keyword. The range keyword allows you to iterate over elements in an array, slice, string, map, or channel.

Here's an example of how to use the range keyword:

numbers := []int{1, 2, 3, 4, 5}

for index, value := range numbers {
    fmt.Println("Index:", index, "Value:", value)
}

In this code, numbers is a slice containing the numbers 1 to 5. The range keyword is used to iterate over each element in the slice. On each iteration, the index and value of the current element are printed.

The output of this code will be:

Index: 0 Value: 1
Index: 1 Value: 2
Index: 2 Value: 3
Index: 3 Value: 4
Index: 4 Value: 5

The range keyword can also be used with strings to iterate over each character in the string, with maps to iterate over key-value pairs, and with channels to iterate over values received from the channel.

Nested Loops

Go supports nested loops, which means you can have a for loop inside another for loop. This is useful when you need to iterate over multiple dimensions or perform repetitive actions within the outer loop.

Here's an example:

for i := 1; i <= 3; i++ {
    for j := 1; j <= 3; j++ {
        fmt.Println(i, j)
    }
}

In this code, we have two nested for loops. The outer loop iterates from 1 to 3, and the inner loop also iterates from 1 to 3. The output of this code will be:

1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3

As you can see, the nested loops allow you to systematically iterate over all possible combinations of the loop variables.

Break and Continue Statements

The break statement is used to exit the loop prematurely. It is often used in conjunction with an if statement to check for a certain condition and break out of the loop when that condition is met.

Here's an example:

for i := 1; i <= 5; i++ {
    if i == 3 {
        break
    }
    fmt.Println(i)
}

In this code, the if i == 3 condition checks if the current value of i is equal to 3. If it is, the break statement is executed, and the loop is exited. The output of this code will be:

1
2

The continue statement is used to skip the rest of the current iteration and move on to the next iteration of the loop.

Here's an example:

for i := 1; i <= 5; i++ {
    if i == 3 {
        continue
    }
    fmt.Println(i)
}

In this code, when the i == 3 condition is true, the continue statement is executed, and the rest of the loop body is skipped. The output of this code will be:

1
2
4
5

Conclusion

That's a wrap on the for loop in Go! We covered the basic syntax of the for loop, how to create infinite loops, the range keyword for iterating over elements, nested loops, and the break and continue statements for controlling loop flow.

The for loop is a powerful tool that allows you to repeat a block of code multiple times. It's an essential construct to master as a Go programmer.

I hope you found this article helpful. Stay tuned for more articles in our Go by Example series!