Golang tutorial - 3 Control Flow (Selection)

Selection is a mechanism to execute certain code based on specified condition. There are four types of condition selection in Go :

• selection using if..
• selection using if...else
• selection using if...else if...else
• selection using switch case

Operators

Before learning selection in Go, let’s take a look at operators that can be used in condition selection :

• ( || ) defines OR logical operator : If there is one or two condition equals true, then the result is true. If all of the conditions are false, the result is false.

  Condition	Condition	Result
  true	true	true
  true	false	true
  false	true	true
  false	false	false

• ( && ) defines AND logical operator : The result equals true if two conditions are true, if one of the conditions are false, the result is false.

  Condition	Condition	Result
  true	true	true
  true	false	false
  false	true	false
  false	false	false

• ( > ) defines greater than operator

• ( >= ) defines greater or equal operator

• ( < ) defines less than operator

• ( <= ) defines less or equal operator

• ( == ) defines equal operator

• ( != ) defines not equal operator

• ( ! ) defines negation of statement

  Condition	Result
  !true	false
  !false	true

Selection using if... statement

The anatomy of if... statement in Go is like this :
if condition { ... }
The code inside the if condition will be executed if the conditions are true.
Here it is the example of using if condition to check whether the number is odd or even.

package main

import (
    "fmt"
)

func main() {
    a := 42
    if a%2 == 0 { //check if value of variable a is an even number
        fmt.Println("This is even number")
    }
}

The output from that code is :

This is even number

Selection using if...else statement

The anatomy of if...else statement is like this :
if condition {
//code
} else {
//code
}
The code inside the if condition will be executed if the conditions are true, otherwise, will be executed inside the else statement.
From the example above, let's add else statement and change the value in a variable.

package main

import (
    "fmt"
)

func main() {
    a := 45
    if a%2 == 0 { //check if value of variable a is an even number
        fmt.Println("This is even number")
    } else {
        fmt.Println("This is odd number")
    }
}

The output from that code is :

This is odd number

Selection using if...else if...else statement

The anatomy of if...else if...else statement is like this :
if condition {
//code
} else if condition {
//code
} else {
//code
}
The code inside if statement will be executed if the conditions are true. Otherwise the code will be executed inside the else if conditions. If there is no conditions are true, the code finally will be executed inside else statement.
The example of using that statement is like this, the code will check the value from grade variable and print out the grade result in alphabet character.

package main

import (
    "fmt"
)

func main() {
    grade := 79
    if grade < 50 {
        fmt.Println("D")
    } else if grade >= 50 && grade < 70 {
        fmt.Println("C")
    } else if grade >= 70 && grade < 80 {
        fmt.Println("B")
    } else if grade >= 80 && grade <= 100 {
        fmt.Println("A")
    } else {
        fmt.Println("undefined")
    }
}

The output from that code is :

B

Selection using switch case statement

The anatomy of switch case statement is like this :
switch expression
case condition:
//code
case condition:
//code
default:
//code

The code will be executed based on case that matched with the defined expression beside switch keyword. If there is no any case is matches. The code inside default keyword will be executed.
The example of using switch case statement can be seen in this code, this code will check the value from user variable and prints welcome message based on user's variable value.

package main

import (
    "fmt"
)

func main() {
    user := "admin"

    switch user {
    case "user":
        fmt.Println("Welcome user !")
    case "manager":
        fmt.Println("Welcome manager!")
    case "admin":
        fmt.Println("Welcome admin!")
    default:
        fmt.Println("Who are you?")
    }
}

The output from that code is :

Welcome admin!

There is fallthrough keyword in switch case selection to execute another code under the matched case. Here is the example

package main

import (
    "fmt"
)

func main() {
    user := "user"

    switch user {
    case "user":
        fmt.Println("Welcome user !")
        fallthrough
    case "manager":
        fmt.Println("Welcome manager!") //this code executed because of fallthrough keyword
    case "admin":
        fmt.Println("Welcome admin!")
    default:
        fmt.Println("Who are you?")
    }
}

The output from that code is :

Welcome user !
Welcome manager!

Notes

In any condition selection using Go. We can apply expression as well.
The example is like this :

package main

import (
    "fmt"
)

func main() {
    if x := 42; x%2 == 0 { //assign expression inside if statement
        fmt.Println("even")
    } else {
        fmt.Println("odd")
    }
}

The output from that code is :

even

This is the example using expression inside switch case selection :

package main

import (
    "fmt"
)

func main() {
    switch user := "manager"; user {
    case "user":
        fmt.Println("Hello user!")
    case "admin":
        fmt.Println("Hello admin!")
    case "manager":
        fmt.Println("Hello manager!")
    default:
        fmt.Println("who are you?")
    }
}

Output :

Hello manager!

Sources

• Learn more about if statement here
• Learn more about switch statement here

I hope this article helpful for helping to learn the Go programming language. If you have any thoughts or feedbacks, you can write it in the discussion section below.