Go Variables and Data Types

Variables store values. In Go, every variable has a type that cannot change.

Declaring Variables

Go has two ways to create a variable:

Example

package main

import "fmt"

func main() {
	var city string = "Karachi"
	var students = 40    // type is inferred as int
	fee := 3500          // short declaration
	fee = 3000

	fmt.Println(city, students, fee)
}

Output

Karachi 40 3000

Form	Where you can use it	Example
`var name type = value`	Anywhere	`var age int = 20`
`var name = value`	Anywhere	`var age = 20`
`name := value`	Only inside functions	`age := 20`

:= creates a new variable. To change a variable that already exists, use plain =.

Zero Values

If you declare a variable without a value, Go gives it a zero value. There are no "empty" or random values in Go.

Example

package main

import "fmt"

func main() {
	var count int
	var price float64
	var name string
	var ready bool
	fmt.Println(count, price, ready)
	fmt.Printf("name is %q\n", name)
}

Output

0 0 false
name is ""

Basic Data Types

Type	Stores	Example	Zero value
`int`	Whole numbers	`42`	`0`
`float64`	Decimal numbers	`99.5`	`0`
`string`	Text	`"Quetta"`	`""`
`bool`	`true` or `false`	`true`	`false`
`rune`	One character (Unicode)	`'A'`	`0`
`byte`	One small number (0 to 255)	`65`	`0`

There are also sized versions such as int8, int64 and float32, but int and float64 are the usual choices.

Seeing a Type

The %T verb of Printf shows a value's type, and %v shows the value itself:

Example

package main

import "fmt"

func main() {
	a := 10
	b := 3.5
	c := "hello"
	d := true
	fmt.Printf("%v is %T\n", a, a)
	fmt.Printf("%v is %T\n", b, b)
	fmt.Printf("%v is %T\n", c, c)
	fmt.Printf("%v is %T\n", d, d)
}

Output

10 is int
3.5 is float64
hello is string
true is bool

Multiple Variables

You can declare several variables on one line:

Example

x, y := 5, 8
var first, last string = "Ayesha", "Khan"

Constants

A constant's value is fixed when the program is compiled. Use const:

Example

package main

import "fmt"

const Institute = "Workownix"
const Pi = 3.14159

func main() {
	fmt.Println(Institute)
	fmt.Println(Pi * 2)
}

Output

Workownix
6.28318

Type Conversion

Go never converts types for you. Write the type name like a function: float64(x), int(y). To turn text into numbers, use the strconv package.

Example

package main

import (
	"fmt"
	"strconv"
)

func main() {
	marks := 45
	total := 60
	percent := float64(marks) / float64(total) * 100
	fmt.Println(percent)

	n, err := strconv.Atoi("123")
	fmt.Println(n+1, err)

	text := strconv.Itoa(2026)
	fmt.Println("Year " + text)
}

Output

75
124 <nil>
Year 2026

strconv.Atoi returns two values: the number and an error. <nil> means there was no error. You will learn more about errors in the functions lesson.

Exercise

What is the value of x after var x int?

nilundefined0A random number