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 → for boolean type.
• "" → (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)

	// %#v means print in golang syntax
}

Reference

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