Lesson 2: Variables¶

Big Picture¶

flowchart LR
    subgraph "Declaration styles"
        A["var name = Go<br/>explicit type"] 
        B["var age = 25<br/>type inference"]
        C["count := 10<br/>short declaration<br/>(functions only)"]
    end
    D["No initializer?"] --> E["Zero value:<br/>int→0 · string→empty · bool→false"]
    F["const pi = 3.14"] -.->|"cannot be reassigned"| G[("Immutable")]

var works anywhere; := is a shortcut only allowed inside functions. Pick := when the type is obvious — it's the idiomatic default.

Concepts¶

Declaration Methods¶

// Explicit type
var name string = "Go"

// Type inference
var age = 25

// Short declaration (inside functions only)
count := 10

Constants¶

const pi = 3.14159
const maxSize = 100

Zero Values¶

Variables declared without initialization get zero values:

Code Walkthrough¶

package main

import "fmt"

func main() {
    var name string = "Go"   // explicit type
    var age = 10             // inferred
    version := 1.23          // short declaration

    var count int            // zero value: 0
    var ready bool           // zero value: false

    fmt.Println(name, age, version, count, ready)
}

Full program: code/02_variables.go.

cd code
go run . variables   # declaration demo
go run . scan        # interactive fmt.Scan demo

Check Your Understanding¶