Understanding For Loops in Golang: The Ultimate Beginners Guide in 2022 with Code Examples

The only way to iterate in Golang is to use the for loop construct. There’s no for-each or a while statement–but we can emulate them with the for loop statement.

sum := 0
for i := 0; i < 10; i++ {
	sum += i
}
fmt.Println(sum)

In this guide will talk about the following topics:

1. What goes into a for loop?
2. How to emulate a for-each statement in Golang
3. How to emulate a while statement in Golang
4. How to emulate an infinite loop without any statements
5. How to exit a for loop

Let’s dive in!

What goes into a for loop?

The basic for loop has three simple components, all separated by semicolons (;).

for i := 0; i < 10; i++ {
	// ...some execution here
}

The first component is the initial statement. This is the area where you typically create a variable with number value.

i := 0;

The second component is the condition expression. At this point of the loop, Golang is going to try to evaluate a statement to determine whether it goes to the final component.

i < 10;

The final component is the called the post statement. After the evaluation passes, and the code with the curly braces ({}) gets executed, the post statement will execute after the iteration.

i++

Here’s the kicker to the components on a for loop in Golang, they’re all optional.

How to emulate a foreach statement in Golang

A foreach loop does not exist in Golang–but you can emulate it with a range statement in the for components!

Here are 3 basic foreach patterns you can use with a range loop.

Example 1. Arrays

Let’s say you have a an array of strings:

cats := []string{"Monkey", "Mr. Whiskers"}

In a foreach statement you should have access to the index of the array & the value.

cats := []string{"Monkey", "Mr. Whiskers"}
fmt.Println(cats)
for i, name := range cats {
	fmt.Println(i, name)
}

The output would look something like this:

0 Monkey
1 Mr. Whiskers

Example 2. Strings

You can also iterate over strings–you’d be iterating over each character within the string value.

for i, ch := range "Mr. Whiskers" {
	fmt.Printf("%#U starts in position %d\n", ch, i)
}

The output would look something like this:

U+004D 'M' starts in position 0
U+0072 'r' starts in position 1
U+002E '.' starts in position 2
U+0020 ' ' starts in position 3
U+0057 'W' starts in position 4
U+0068 'h' starts in position 5
U+0069 'i' starts in position 6
U+0073 's' starts in position 7
U+006B 'k' starts in position 8
U+0065 'e' starts in position 9
U+0072 'r' starts in position 10
U+0073 's' starts in position 11

Example 3. Maps

cats := map[int]string{
	1: "Mr. Whiskers",
	2: "Monkey",
	3: "Smokey",
}
for k, v := range cats {
	fmt.Println(k, v)
}

Skip index or value

You can skip the index or value of a range loop by using an underscore (_).

for i, _ := range cats
for _, value := range cats

How to emulate a while statement in Golang

To make a while loop in Golang, you’ll need to skip the first and third component of a for loop structure.

a := 1
for a < 10 {
	a *= 2
}

You can see in the for loop structure, it’s just the evaluation and init or post statements, and no semicolons (;)

How to emulate an infinite loop without any statements

All components in a for loop are optional. So you have have zero statements or conditions!

sum := 0
for {
    sum++ // repeated forever
}

I haven’t come across a scenario where this is useful, but it’s there just incase.

How to exit a for loop

To break a loop you need to use the special keyword break inside the curly braces ({}) of a for loop.

sum := 0
for {
	if sum > 4 {
		break;
	}
	sum++

}
fmt.Println(sum)

Do not confuse break with the another special keyword called continue.

The keyword continue in a for loop only skips to the next iteration of the loop. It does not completely break the loop in Golang.

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