Control Flow

If Statement

One notable distinction between if statements in Go and those in other programming languages is the capability to declare variables scoped exclusively to the condition and both the if and else blocks. This feature enables the creation of variables accessible only within their intended scope, enhancing code clarity and reducing potential side effects. Upon concluding the series of if/else statements, the variable's scope does not exist anymore, producing a compilation error.

Variable Spoce to If

if n := rand.Intn(10); n == 0 {
    fmt.Println("That's too low")
} else if n > 5 {
    fmt.Println("That's too big:", n)
} else {
    fmt.Println("That's a good number:", n)
}

for

In Go for is the only looping keyword in the language. The for loop can be used in four formats:

A Complete For

The if statement has three parts, separated by semicolons: initialization, comparison, and increment. Go allows you to leave out one or more of the three parts of the for statement.

Ways to Create a Complete For

for i := 0; i <= 9; i ++ {
    fmt.Println(i)
}

for i := 0; i <= 9; {
    fmt.Println(i)
    i++
}

i := 0
for ; i <=9; i++ {
    fmt.Println(i)
}

A Condition-Only For

It's a for loop with just the comparison part.

Just Comparison for

i := 1
for i < 100 {
    fmt.Println(i)
    i++
}

An infinite For

A for loop without any part.

A infinite for

for {
    fmt.Println("Hello")
}

For-Range

A for loop iterating over elements in some of Go’s built-in types. With this for, the first variable is the position in the data structure being iterated. Each time the for-range loop iterates with the variable data, it copies the value from the original variable to the value variable. Modifying the value variable will not modify the value in the compound type.

Iterating over built-in types

data := []int{1, 2, 3, 4, 5, 6, 7}
for i, v := range data {
    fmt.Println(i, v)
}
for _, v := range data {
    fmt.Println(v)
}

// Just the keys
dicData := map[string]int{"Key1": 1, "Key2": 2}
for k := range uniqueNames {
    fmt.Println(k)
}

for k, v := range m {
    fmt.Println(k, v)
}

strData := "hello"
for i, r := range strData {
    fmt.Println(i, r, string(r))
}

break and continue keywords

In Go, break and continue keywords exist and behave similarly to other languages like C, and JavaScript. The break stops the loop, while the continue skips to the next iteration.

Labeling For Statements

Labels in Go are used in nested for loops and want to skip over an iteration of an outer loop. Labels are indented to the same level as the surrounding function. Labels are always indented to the same level as the braces for the block.

Using Labels

run command

go run src/control_flow/labels.go
Start sample:  hello
h
e
l
Start sample:  apple_π!
a
p
p
l

package main

import "fmt"

func main() {
    samples := []string{"hello", "apple_π!"}
outer:
    for _, sample := range samples {
        fmt.Println("Start sample: ", sample)
        for _, r := range sample {
            fmt.Println(string(r))
            if r == 'l' {
                continue outer
            }
        }
    }
}

switch

Switch statements also have scoped variables exclusively to the block condition. Also, it's possible to combine multiple matches with commas. There are empty cases that mean nothing happens. You can switch on any type that can be compared with ==. Go supports blank switches that allow to use any boolean comparison for each case.

Using Switch

run command

$ go run src/control_flow/switch.go
Monday :(
IT'S FRIDAY FINALLY!
Today is  Tuesday
Is not a day

Now blank switch:
Monday is a short day!
Friday is a short day!
Tuesday is a long day!
Corinthians is not a day!

src/control_flow/switch.go

package main

import "fmt"

func main() {
    days := []string{"Monday", "Friday", "Tuesday", "Corinthians"}

    for _, day := range days {
        switch day {
        case "Monday":
            fmt.Println("Monday :(")
        case "Tuesday", "Wednesday", "Thursday":
            fmt.Println("Today is ", day)
        case "Friday":
            fmt.Println("IT'S FRIDAY FINALLY!")
        case "Saturday", "Sunday":
        default:
            fmt.Println("Is not a day")
        }
    }
    fmt.Println()
    fmt.Println("Now blank switch:")

    for _, word := range days {
        switch wordLen := len(word); {
        case wordLen <= 6:
            fmt.Println(word, "is a short day!")
        case wordLen > 6 && wordLen <= 10:
            fmt.Println(word, "is a long day!")
        default:
            fmt.Println(word, "is not a day!")
        }
    }
}