Declaring Variables with var

Basic var Declaration

The var keyword declares a variable with an explicit name and type: 'var age int'. Until you assign it a value, it holds the zero value for that type -- 0 for numbers, "" for strings, false for booleans. This is different from many languages where an uninitialized variable is undefined or an error.

Example: Basic var Declaration

package main

import "fmt"

func main() {
	var age int
	var name string
	fmt.Println("age:", age)
	fmt.Println("name:", name)
}

Declaring and Initializing Together

You can supply an initial value in the same line as a var declaration: 'var age int = 30'. If an initializer is present, Go can often infer the type, letting you drop the explicit type entirely and write 'var age = 30'.

Example: Declaring and Initializing Together

package main

import "fmt"

func main() {
	var age int = 30
	var city = "Bengaluru"
	fmt.Println(age, city)
}

Declaring Multiple Variables

A single var block can declare several variables at once using parentheses, which keeps related declarations grouped and readable, especially at the top of a file for package-level variables.

Note: Grouping related variables in a var block is a common way to keep package-level declarations organized.

Example: Declaring Multiple Variables

package main

import "fmt"

var (
	appName    = "Inventory"
	appVersion = "1.0"
	maxItems   = 100
)

func main() {
	fmt.Println(appName, appVersion, maxItems)
}

Package-Level vs Local Variables

Variables declared with var inside a function are local to that function, while var declarations outside any function, at the top level of a file, become package-level variables visible throughout the package. Package-level var is one of the few places Go allows a variable to exist without being immediately used.

Example: Package-Level vs Local Variables

package main

import "fmt"

var counter int

func increment() {
	counter++
}

func main() {
	increment()
	increment()
	fmt.Println("counter:", counter)
}