Variables

Use var keyword to declare a variable. Here are the rules:

• The name of the identifier must begin with a letter or an underscore(_). And the names may contain the letters ‘a-z’ or ’A-Z’ or digits 0-9 as well as the character ‘_’.
• The name of the identifier should not start with a digit.
• The name of the identifier is case sensitive.
• Keywords is not allowed to use as an identifier name.
• There is no limit on the length of the name of the identifier.

// Valid identifiers:
_geeks23
geeks
gek23sd
Geeks
geeKs
geeks_geeks

// Invalid identifiers:
212geeks
if
default

Here is an example:

package main
import "fmt"

func main() {

 var name = "GeeksforGeeks"
  
}

The identifier represented by the underscore character(_) is known as a blank identifier. It is used as an anonymous placeholder instead of a regular identifier, and it has a special meaning in declarations, as an operand, and in assignments.

data type of variable

To mention datatype of the variable write the type after the variable name and seperate them with a space.

var name string, age int
var c, python, java bool

Here is an example:

package main

import "fmt"

// package level variables
var c, python, java bool

func main() {
	// function level variable 
	var i int
	fmt.Println(i, c, python, java)
}

It will produce the following output:

0 false false false

Variables with initializers

A var declaration can include initializers, one per variable. If an initializer is present, the type can be omitted; the variable will take the type of the initializer.

package main

import "fmt"

var i, j int = 1, 2

func main() {
	var c, python, java = true, false, "no!"
	fmt.Println(i, j, c, python, java)
}

The output of the above code is:

1 2 true false no

The first value true goes to the first variable c, the second value false goes to the second variable python, and the last value "no" goes to variable java.

The number of variables on the left side of the =, and the number of values on the right side of the =, must be same. Otherwise you will get an exception.

Short variable declarations

Inside a function, the := short assignment statement can be used in place of a var declaration with implicit type.

package main

import "fmt"

func main() {
	var i, j int = 1, 2
	k := 3
	c, python, java := true, false, "no!"

	fmt.Println(i, j, k, c, python, java)
}

Outside a function, every statement begins with a keyword (var, func, and so on) and so the := construct is not available.

Zero values

Variables declared without an explicit initial value are given their zero value.

• 0 for numeric types,
• false for the boolean type, and
• "" (the empty string) for strings.

package main

import "fmt"

func main() {
	var i int
	var f float64
	var b bool
	var s string
	fmt.Printf("%v %v %v %q\n", i, f, b, s)
}

Output:

0 0 false ""