Default Zero Values in Go

In Go (also referred to as Golang), when you declare a variable without explicitly initializing it with a value, it is given a default value. This default value is called the "zero value" for its type. Here's what the zero values are for some common types in Go:

int: 0
float64: 0.0
bool: false
string: "" (empty string)
pointer: nil
slice: nil
map: nil
channels: nil
functions: nil
interfaces: nil
array: Array of appropriate length filled with zero values for the array's type. For example, the zero value of [3]int is [0, 0, 0].

Here's a simple example:

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)
}

When run, this program will print:

0 0 false ""

Exercises:

Basic Zero Values:
- Declare a variable of type *int and print its value.
- Declare a variable of type []string and print its value.
- Declare a variable of type map[string]int and print its value.
Struct Zero Values:
- Define a struct Person with Name as a string and Age as an int.
- Declare a variable of type Person and print its value.
Zero Value Functionality:
- Declare a slice of ints.
- Without initializing the slice, try to append a value to it and print the result.

Solutions:

Basic Zero Values:

package main

import "fmt"

func main() {
    var ptr *int
    var slice []string
    var m map[string]int
    fmt.Println(ptr, slice, m)
}

Output:

<nil> [] <nil>

Struct Zero Values:

package main

import "fmt"

type Person struct {
    Name string
    Age  int
}

func main() {
    var p Person
    fmt.Println(p)
}

Output:

{ 0}

Zero Value Functionality:

package main

import "fmt"

func main() {
    var numbers []int
    numbers = append(numbers, 5)
    fmt.Println(numbers)
}

Output:

[5]

This demonstrates that even though the zero value of a slice is nil, you can still use append() with it.

Default Zero Values in Go

Table of contents

Exercises:

Solutions: