Contact Management System

Learn contact management system through an executable example, then connect the small demonstration to production code.

A contact manager stores people by a stable identifier and supports create, read, update and delete operations. Use a map for the in-memory index and sort keys to produce deterministic output.

This learning version updates one contact and prints all remaining contacts in alphabetical key order.

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

Expansion: implement a CLI menu or REST endpoints, JSON persistence, unique identifiers, search and field validation. Test updates and deletions of nonexistent IDs.

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

Go code

package main

import (
	"fmt"
	"sort"
)

type Contact struct{ Name, Email string }

func main() {
	contacts := map[string]Contact{"a1": {"Asha", "asha@example.test"}, "b2": {"Bala", "bala@example.test"}}
	contacts["b2"] = Contact{"Bala", "bala.new@example.test"}
	keys := make([]string, 0, len(contacts))
	for key := range contacts {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	for _, key := range keys {
		fmt.Println(key, contacts[key].Name, contacts[key].Email)
	}
}

Output

a1 Asha asha@example.test
b2 Bala bala.new@example.test

The map starts with two contacts. Reassigning b2 changes its email, and sorting the keys ensures that a1 prints before b2.

• A person’s display name should not automatically be treated as a unique ID.
• Validate contact fields and consider privacy, backups and delete behavior before deployment.

Implement Add, Find, Update and Delete methods and verify missing-ID responses.

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

You have practiced Contact Management System 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.