Basic Syntax: Packages, Functions, and Variables

Basic Syntax: Packages, Functions, and Variables

This lesson explains how Go programs are structured and how to declare values, variables, and functions.

Packages

Every Go source file starts with a package declaration. A package groups related Go files together.

package main

The main package is used for executables. Other packages are reusable libraries.

Imports

Use import to bring in code from the standard library or external modules.

import "fmt"

Variables

Declare variables with explicit types or let Go infer the type from the value.

var a int    // zero-value 0
var b string // zero-value ""
var c = true // type inferred

Go gives each uninitialized variable a zero value: 0, "", false, or nil for pointers, slices, maps, and interfaces.

Short variable declaration

Inside functions, use := for shorter declarations.

x := 42
msg := "Go is fun"

Functions

Functions are declared with func, and parameters and return types are explicit.

func add(a, b int) int {
    return a + b
}

func main() {
    fmt.Println(add(3, 4))
}

Functions can also return multiple values, which is common in Go.

func swap(a, b string) (string, string) {
    return b, a
}