Zero Value

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

Default value are different for different types of variables.

The default value for a type is called its “zero value”.

The zero values are:

• 0 for numeric types
• false the boolean type.
• "" (the empty string) for string type.
• nil for pointers, functions, interfaces, slices, channels, and maps.

package main

import "fmt"

func main() {

    var i int
    var f float64
    var b bool
    var str string
    var sl []int

    fmt.Printf("%#v\n", i)   // 0
    fmt.Printf("%#v\n", f)   // 0
    fmt.Printf("%#v\n", b)   // false
    fmt.Printf("%#v\n", str) // ""
    fmt.Printf("%#v\n", sl)  // []int(nil)

    // the %#v means print in golang syntax

}

Reference

The Go Programming Language Specification - The Go Programming Language#The_zero_value