For Loops

In Go, for loops are the only loop construct available. There are no while or do while loops in Go, the canonical way to do these sort of loops is via for loops.

The basic structure of a for loop in Go is as follows:

for.go

for i := 1; i <= 5; i++ {
    fmt.Println("Count:", i)
}

This will print:

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

Similar to JavaScript/TypeScript, there are three parts to the for loop:

1. Initialization: i := 1 - This initializes the loop variable i to 1.
2. Condition: i <= 5 - This is the condition that is checked before each iteration of the loop. If it evaluates to true, the loop body will execute.
3. Post Statement: i++ - This is executed after each iteration of the loop body. In this case, it increments i by 1. The loop will continue until the condition evaluates to false.

However unlike JavaScript/TypeScript, parts of the for loop can be omitted.

Different ways to use for loops

The possibility to omit parts of the for loop allows you to create all sorts of loops like while loops and inifinite loops.

This flexibility is one of the reasons why for loops are the only loop construct in Go.

While Loops

for_while.go

x := 0
for x < 5 {
    fmt.Println("Count:", x)
    x++
}

Note that the initialization and post statement parts are omitted.

Infinite Loops

for_infinite.go

for {
    fmt.Println("This will run forever!")
}

Note the absence of any condition in the for statement. You can use break to exit the loop if needed.

Do While Loops

for_do_while.go

x := 0
for {
    fmt.Println("Count:", x)
    x++
    if x >= 5 {
        break
    }
}

range keyword

You can use the range keyword to iterate over arrays, slices, maps, and channels in Go.

This is similar to the for...of loop in JavaScript/TypeScript.

Iterating over Strings

for_range_string.go

str := "Hello"
for i, v := range str {
    fmt.Printf("Index: %d, Value: %c\n", i, v)
}

This will print:

Index: 0, Value: H
Index: 1, Value: e
Index: 2, Value: l
Index: 3, Value: l
Index: 4, Value: o

Note that the value v is of type rune, which is an alias for int32. This is because Go uses UTF-8 encoding for strings, and rune can represent any Unicode character.

Iterating over Arrays and Slices

for_range_array.go

arr := [5]int{1, 2, 3, 4, 5}
for i, v := range arr {
    fmt.Printf("Index: %d, Value: %d\n", i, v)
}

This will print:

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

Iterating over Maps

for_range_map.go

myMap := map[string]int{"apple": 1, "banana": 2}
for k, v := range myMap {
    fmt.Printf("Key: %s, Value: %d\n", k, v)
}

This will likely print:

Key: apple, Value: 1
Key: banana, Value: 2

Danger

Unlike JavaScript/TypeScript, the order of iteration over maps is not guaranteed in Go. The order may vary between different runs of the program.

If you need to iterate over a map in a specific order, you can use a slice to store the keys, sort them and then iterate over the sorted keys and use them to access the map.

break and continue

Like JavaScript/TypeScript, you can use break and continue statements in Go to control the flow of loops.

for_break_continue.go

for i := 1; i <= 5; i++ {
    if i == 3 {
        continue // Skip the rest of the loop when i is 3
    }
    if i == 5 {
        break // Exit the loop when i is 5
    }
    fmt.Println("Count:", i)
}

This will print:

Count: 1
Count: 2
Count: 4

Labels

Like JavaScript/TypeScript, you can use labels to break out of nested loops.