Variables & Types

package main

import "fmt"

func main() {
    // Long form: var name type = value
    var name string = "Alice"
    var age int = 30

    // Short form: := infers the type (most common inside functions)
    city := "Paris"
    pi := 3.14159

    // Zero values — Go initializes everything
    var i int       // 0
    var f float64   // 0.0
    var b bool      // false
    var s string    // ""
    fmt.Println(i, f, b, s)

    // Multiple assignment
    x, y := 1, 2
    x, y = y, x  // swap
    fmt.Println(x, y)

    // Constants
    const MaxSize = 1024
    const Pi = 3.14159
    const Greeting = "Hello"

    // iota — auto-incrementing constant
    const (
        Sunday = iota  // 0
        Monday         // 1
        Tuesday        // 2
        Wednesday      // 3
    )

    fmt.Println(name, age, city, pi)
    fmt.Println(Sunday, Monday, Tuesday, Wednesday)
}

package main

import "fmt"

func main() {
    // Basic types
    var i8 int8 = 127         // -128 to 127
    var i32 int32 = 2147483647
    var u64 uint64 = 18446744073709551615
    var f32 float32 = 3.14
    var f64 float64 = 3.141592653589793

    // Type conversion must be explicit
    var x int = 42
    var y float64 = float64(x)  // explicit conversion required
    var z int = int(y)

    // Strings
    s := "Hello, 世界"
    fmt.Println(len(s))         // byte count (not rune count!)
    fmt.Println([]rune(s))      // convert to rune (Unicode codepoints)

    // String concatenation
    first := "Hello"
    second := "World"
    combined := first + ", " + second + "!"
    fmt.Println(combined)

    // Rune (unicode codepoint)
    r := 'A'   // rune (int32)
    fmt.Printf("%c %d\n", r, r)   // A 65

    _ = i8; _ = i32; _ = u64; _ = f32; _ = f64; _ = z  // avoid "declared and not used"
}