If Statement

If statements are used to specify whether a block of code should be executed or not depending on a given condition.

Following is the syntax of if statements in Golang -

if(condition) {
	// Code to be executed if the condition is true.
}

Here is a simple example -

package main
import "fmt"

func main() {
	var x = 25
	if(x % 5 == 0) {
		fmt.Printf("%d is a multiple of 5\n", x)
	}
}
# Output
25 is a multiple of 5

Note that, You can omit the parentheses () from an if statement in Golang, but the curly braces {} are mandatory -

var y = -1
if y < 0 {
	fmt.Printf("%d is negative\n", y)
}

You can combine multiple conditions using short circuit operators && and || like so -

var age = 21
if age >= 17 && age <= 30 {
	fmt.Println("My Age is between 17 and 30")
}	

If-Else Statement

An if statement can be combined with an else block. The else block is executed if the condition specified in the if statement is false -

if condition {
	// code to be executed if the condition is true
} else {
	// code to be executed if the condition is false
}

Here is a simple example -

package main
import "fmt"

func main() {
	var age = 18
	if age >= 18 {
		fmt.Println("You're eligible to vote!")
	} else {
		fmt.Println("You're not eligible to vote!")
	}
}
# Output
You're eligible to vote!

If-Else-If Chain

if statements can also have multiple else if parts making a chain of conditions like this -

package main
import "fmt"

func main() {
	var BMI = 21.0
	if BMI < 18.5 {
		fmt.Println("You are underweight");
	} else if BMI >= 18.5 && BMI < 25.0 {
		fmt.Println("Your weight is normal");
	} else if BMI >= 25.0 && BMI < 30.0 {
		fmt.Println("You're overweight")
	} else {
		fmt.Println("You're obese")
	}
}
# Output
Your weight is normal

If with a short statement

An if statement in Golang can also contain a short declaration statement preceding the conditional expression -

if n := 10; n%2 == 0 {
	fmt.Printf("%d is even\n", n)
} 

The variable declared in the short statement is only available inside the if block and it’s else or else-if branches -

if n := 15; n%2 == 0 {
	fmt.Printf("%d is even\n", n)
} else {
	fmt.Printf("%d is odd\n", n)
}

Note that, If you’re using a short statement, then you can’t use parentheses. So the following code will generate a syntax error -

// You can't use parentheses when `if` contains a short statement
if (n := 15; n%2 == 0) { // Syntax Error

}

Switch Statement

A Switch statement takes an expression and matches it against a list of possible cases. Once a match is found, it executes the block of code specified in the matched case.

Here is a simple example of switch statement -

package main
import "fmt"

func main() {
	var dayOfWeek = 6
	switch dayOfWeek {
		case 1: fmt.Println("Monday")
		case 2: fmt.Println("Tuesday")
		case 3: fmt.Println("Wednesday")
		case 4: fmt.Println("Thursday")
		case 5: fmt.Println("Friday")
		case 6: {
			fmt.Println("Saturday")
			fmt.Println("Weekend. Yaay!")
		}
		case 7: {
			fmt.Println("Sunday")
			fmt.Println("Weekend. Yaay!")
		}
		default: fmt.Println("Invalid day")
	}
}
# Output
Saturday
Weekend. Yaay!

Go evaluates all the switch cases one by one from top to bottom until a case succeeds. Once a case succeeds, it runs the block of code specified in that case and then stops (it doesn’t evaluate any further cases).

This is contrary to other languages like C, C++, and Java, where you explicitly need to insert a break statement after the body of every case to stop the evaluation of cases that follow.

If none of the cases succeed, then the default case is executed.

Switch with a short statement

Just like if, switch can also contain a short declaration statement preceding the conditional expression. So you could also write the previous switch example like this -

switch dayOfWeek := 6; dayOfWeek {
	case 1: fmt.Println("Monday")
	case 2: fmt.Println("Tuesday")
	case 3: fmt.Println("Wednesday")
	case 4: fmt.Println("Thursday")
	case 5: fmt.Println("Friday")
	case 6: {
		fmt.Println("Saturday")
		fmt.Println("Weekend. Yaay!")
	}
	case 7: {
		fmt.Println("Sunday")
		fmt.Println("Weekend. Yaay!")
	}
	default: fmt.Println("Invalid day")
}

The only difference is that the variable declared by the short statement (dayOfWeek) is only available inside the switch block.

Combining multiple Switch cases

You can combine multiple switch cases into one like so -

package main
import "fmt"

func main() {
	switch dayOfWeek := 5; dayOfWeek {
		case 1, 2, 3, 4, 5:
			fmt.Println("Weekday")
		case 6, 7:
			fmt.Println("Weekend")
		default:
			fmt.Println("Invalid Day")		
	}
}
# Output
Weekday

This comes handy when you need to run a common logic for multiple cases.

Switch with no expression

In Golang, the expression that we specify in the switch statement is optional. A switch statement without an expression is same as switch true. It evaluates all the cases one by one, and runs the first case that evaluates to true -

package main
import "fmt"

func main() {
	var BMI = 21.0 
	switch {
		case BMI < 18.5:
			fmt.Println("You're underweight")
		case BMI >= 18.5 && BMI < 25.0:
			fmt.Println("Your weight is normal")
		case BMI >= 25.0 && BMI < 30.0:
			fmt.Println("You're overweight")
		default:
			fmt.Println("You're obese")	
	}
}

Switch without an expression is simply a concise way of writing if-else-if chains.

For Loop

A loop is used to run a block of code repeatedly. Golang has only one looping statement - the for loop.

Following is the generic syntax of for loop in Go -

for initialization; condition; increment {
	// loop body
}

The initialization statement is executed exactly once before the first iteration of the loop. In each iteration, the condition is checked. If the condition evaluates to true then the body of the loop is executed, otherwise, the loop terminates. The increment statement is executed at the end of every iteration.

Here is a simple example of a for loop -

package main
import "fmt"

func main() {
	for i := 0; i < 10; i++ {
		fmt.Printf("%d ", i)
	}
}
# Output
0 1 2 3 4 5 6 7 8 9 

Unlike other languages like C, C++, and Java, Go’s for loop doesn’t contain parentheses, and the curly braces are mandatory.

Note that, both initialization and increment statements in the for loop are optional and can be omitted

  • Omitting the initialization statement

    package main
    import "fmt"
    
    func main() {
        i := 2
        for ;i <= 10; i += 2 {
            fmt.Printf("%d ", i)
        }
    }
    
    # Output
    2 4 6 8 10 
    
  • Omitting the increment statement

    package main
    import "fmt"
    
    func main() {
        i := 2
        for ;i <= 20; {
            fmt.Printf("%d ", i)
            i *= 2
        }
    }
    
    # Output
    2 4 8 16
    

    Note that, you can also omit the semicolons from the for loop in the above example and write it like this -

    package main
    import "fmt"
    
    func main() {
        i := 2
        for i <= 20 {
            fmt.Printf("%d ", i)
            i *= 2
        }
    }   
    

    The above for loop is similar to a while loop in other languages. Go doesn’t have a while loop because we can easily represent a while loop using for.

Finally, You can also omit the condition from the for loop in Golang. This will give you an infinite loop -

package main

func main() {
	// Infinite Loop
	for {
	}
}

break statement

You can use break statement to break out of a loop before its normal termination. Here is an example -

package main
import "fmt"

func main() {
	for num := 1; num <= 100; num++ {
		if num%3 == 0 && num%5 == 0 {
			fmt.Printf("First positive number divisible by both 3 and 5 is %d\n", num)
			break
		}
	}
}
# Output
First positive number divisible by both 3 and 5 is 15

continue statement

The continue statement is used to stop running the loop body midway and continue to the next iteration of the loop.

package main
import "fmt"

func main() {
	for num := 1; num <= 10; num++ {
		if num%2 == 0 {
			continue;
		}
		fmt.Printf("%d ", num)
	}
}
# Output
1 3 5 7 9 

Conclusion

That’s all folks. In this article, you learned how to work with control flow statements like if, switch and for in Golang.

In the next article, You’ll learn how to define functions in Go. See you in the next post!

Next Article: Introduction to Functions in Go