Go variables and constants

Go is a statically typed programming language, so we must declare variable type every time we use it.

Go basics

There are three ways to declare variables.

• First, declaring variables with datatype. In this case, we are assigning the datatype explicitly.

package main

import "fmt"

func main() {
  var name string
  var lastname string = "Racer"
  var age int = 20

  name = "Speed"

  fmt.Printf("Name : %s, Type : %T\n", name, name)
  fmt.Printf("Lastname : %s, Type : %T\n", lastname, lastname)
  fmt.Printf("Age: %d, Type: %T\n", age, age)
}

Output:

Name : Speed, Type : string
Lastname : Racer, Type : string
Age: 20, Type: int

• Second, using only var, and we don’t specify a datatype for variables; the type will be implicitly taken from the assigned value.

package main

import "fmt"

func main() {
  var name = "Speed"
  var lastname= "Racer"
  var age= 20

  fmt.Printf("Name : %s, Type : %T\n", name, name)
  fmt.Printf("Lastname : %s, Type : %T\n", lastname, lastname)
  fmt.Printf("Age: %d, Type: %T\n", age, age)
}

The output will be the same as above.

• Third, the shorthand syntax. We use := to declare the variable and assign the datatype implicitly. The data type is obtained depending on the value assigned.

package main

import "fmt"

func main() {
  name := "Speed"
  lastname := "Racer"
  age := 20

  fmt.Printf("Name : %s, Type : %T\n", name, name)
  fmt.Printf("Lastname : %s, Type : %T\n", lastname, lastname)
  fmt.Printf("Age: %d, Type: %T\n", age, age)
}

Zero values

Every time we declare a variable without assigning a value, the value of those variables will be set to zero-value according to the datatype used.

package main

import "fmt"

func main() {
  var name string
  var lastname string
  var age int

  fmt.Printf("Name : %s, Type : %T\n", name, name)
  fmt.Printf("Lastname : %s, Type : %T\n", lastname, lastname)
  fmt.Printf("Age: %d, Type: %T\n", age, age)
}

Output:

Name : , Type : string
Lastname : , Type : string
Age: 0, Type: int

String variables: name and lastname will be “”, and age (int — 8 bits) will be 0.

Constants

To declare constants in Go, we use the keyword const. Constants obtain their datatype depending on the assigned value.

package main

import "fmt"

const PI = 3.14
const PREFIX = "variable-"

func main() {
  fmt.Printf("PI     = %v, Type : %T\n", PI, PI)
  fmt.Printf("PREFIX = %v, Type : %T\n", PREFIX, PREFIX)
}

Output:

PI     = 3.14, Type : float64
PREFIX = variable-, Type : string