Struct Programs

Learn struct programs through an executable example, then connect the small demonstration to production code.

Structs group related fields, and methods let you attach behavior to a named type. For basic record processing, initialize a struct and compute a derived result.

The example models a rectangle and calculates area through a value-receiver method that does not mutate the original.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

type Rectangle struct{ Width, Height int }

func (r Rectangle) Area() int { return r.Width * r.Height }
func main()                   { r := Rectangle{Width: 5, Height: 3}; fmt.Println("Area:", r.Area()) }

Output

Area: 15

The Rectangle literal stores width five and height three. The Area method multiplies them, so the displayed result is 15.

• Go uses methods on types, not class inheritance.
• A value receiver receives a copy of its receiver; mutations inside it do not update the original struct.

Add a Perimeter method and print the rectangle’s perimeter.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Struct Programs in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.