if / else Statements

Basic if / else

An if statement runs a block only when its condition evaluates to true, and an optional else block runs otherwise. Unlike C or Java, the condition is never wrapped in parentheses, and the braces are always required, even for a single statement.

Note: Go never requires (or wants) parentheses around the condition.

Example: Basic if / else

package main

import "fmt"

func main() {
	age := 20
	if age >= 18 {
		fmt.Println("adult")
	} else {
		fmt.Println("minor")
	}
}

else if Chains

Multiple conditions can be chained with 'else if', evaluated top to bottom until one is true, falling through to a final else if none match -- useful for handling several mutually exclusive cases.

Example: else if Chains

package main

import "fmt"

func main() {
	score := 72
	if score >= 90 {
		fmt.Println("Grade A")
	} else if score >= 75 {
		fmt.Println("Grade B")
	} else if score >= 60 {
		fmt.Println("Grade C")
	} else {
		fmt.Println("Grade F")
	}
}

if with an Init Statement

Go lets you run a short statement before the condition, separated by a semicolon, most often used to assign a value and immediately test it -- a pattern very common with functions that return a value and an error.

Note: Variables declared in an if's init statement are only visible within that if/else chain.

Example: if with an Init Statement

package main

import "fmt"

func half(n int) (int, bool) {
	if n%2 != 0 {
		return 0, false
	}
	return n / 2, true
}

func main() {
	if result, ok := half(10); ok {
		fmt.Println("half is:", result)
	} else {
		fmt.Println("not evenly divisible")
	}
}

Boolean Expressions

Conditions combine comparisons with && (and), || (or), and ! (not), just like most C-family languages, and Go short-circuits these operators, stopping evaluation as soon as the result is determined.

Example: Boolean Expressions

package main

import "fmt"

func main() {
	age := 25
	hasID := true
	if age >= 18 && hasID {
		fmt.Println("entry allowed")
	}
}