Data Types in Go

var b bool   = true              // false by default
var s string = "Hello, Go"      // "" by default, immutable
var r rune   = 'A'              // int32 alias — Unicode code point
var by byte  = 255              // uint8 alias — raw byte

var i int      // 0
var f float64  // 0.0
var s string   // ""
var b bool     // false
var p *int     // nil

// Full form — explicit type
var name string = "Go"
 
// Type inferred from value
var name = "Go"
 
// Short declaration — inside functions only
name := "Go"
 
// Multiple variables
var x, y int = 1, 2
a, b := 10, "hello"
 
// Block declaration
var (
    host string = "localhost"
    port int    = 8080
    tls  bool   = true
)

var i int = 42
var f float64 = float64(i)   // must be explicit
var u uint = uint(f)
 
// string ↔ int — NOT with a cast, use strconv
s := strconv.Itoa(42)        // int → string "42"
n, err := strconv.Atoi("42") // string → int 42
 
// string(65) converts a rune, NOT an integer to its digits
fmt.Println(string(65))      // "A"  ← common mistake!
fmt.Println(strconv.Itoa(65)) // "65" ← correct

n := 42
fmt.Printf("%d %b %o %x %X\n", n, n, n, n, n)
// 42 101010 52 2a 2A
 
pi := math.Pi
fmt.Printf("%f %.2f %e %g\n", pi, pi, pi, pi)
// 3.141593 3.14 3.141593e+00 3.141592653589793
 
s, r := "hello", 'A'
fmt.Printf("%s %q %c %U\n", s, s, r, r)
// hello "hello" A U+0041
 
type Person struct{ Name string; Age int }
p := Person{"John", 25}
fmt.Printf("%v\n%+v\n%#v\n", p, p, p)
// {John 25}
// {Name:John Age:25}
// main.Person{Name:"John", Age:25}