# Go Fundamentals

# Concept

A Go program is a package, a set of imports, and a list of declarations. There is no implicit global scope beyond the package, no header files, and exactly one way to format code (gofmt). Variables are statically typed, but the type is usually inferred rather than written out.

# Explanation

Declare a variable with var name Type or, inside a function, with name := value — the := form infers the type from the right-hand side. Both forms produce a fully-typed variable; Go never falls back to a dynamic “any” type unless you ask for one with any.

Control flow has three shapes, and no more: if, for, and switch. There is no while — for alone covers it. There are no parentheses around the condition, but the braces are mandatory even for a single statement.

func classify(n int) string {
    if n < 0 {
        return "negative"
    }

    for n > 9 {
        n -= 10
    }

    switch n {
    case 0:
        return "zero"
    default:
        return "single digit"
    }
}

Every .go file lives in exactly one package, declared at the top with package name. An executable program has a package main with a func main() — that’s the entry point go run looks for.

# Usage

package main

import "fmt"

func classify(n int) string {
    if n%2 == 0 {
        return "even"
    }
    return "odd"
}

func main() {
    fmt.Println(classify(4)) // "even"
    fmt.Println(classify(7)) // "odd"
}

Compile and run this with go run main.go, or build a binary with go build. No project file beyond go.mod is required to get started.

Go won’t silently convert an int to a string for you — "n = " + n is a compile error. To turn a number into its decimal string, use strconv.Itoa:

import "strconv"

strconv.Itoa(42) // "42"

# Exercise

Implement FizzBuzz(n int) string: return "Fizz" if n is divisible by 3, "Buzz" if divisible by 5, "FizzBuzz" if divisible by both, and the decimal string of n otherwise.