Building a Calculator Console Application

Project Overview

We'll build a fully functional calculator with the following features:

• Addition, Subtraction, Multiplication, Division
• Error handling (division by zero, invalid input)
• Continue or exit options
• Clean and user-friendly interface

Step 1: Create the Project Structure

Calculator/
├── Program.cs
├── Calculator.cs
└── Calculator.csproj

Step 2: The Calculator Class

Create a separate class to handle calculations:

using System;

public class Calculator
{
    public double Add(double a, double b) => a + b;
    public double Subtract(double a, double b) => a - b;
    public double Multiply(double a, double b) => a * b;
    
    public double Divide(double a, double b)
    {
        if (b == 0)
            throw new DivideByZeroException("Cannot divide by zero!");
        return a / b;
    }
}

Step 3: The Main Program

using System;

class Program
{
    static void Main()
    {
        Console.Title = "Calculator App";
        Calculator calculator = new Calculator();
        
        while (true)
        {
            Console.Clear();
            Console.WriteLine("=== CALCULATOR ===\n");
            
            // Display menu
            Console.WriteLine("Select operation:");
            Console.WriteLine("1. Addition (+)");
            Console.WriteLine("2. Subtraction (-)");
            Console.WriteLine("3. Multiplication (*)");
            Console.WriteLine("4. Division (/)");
            Console.WriteLine("5. Exit");
            Console.Write("\nEnter your choice: ");
            
            string choice = Console.ReadLine();
            
            if (choice == "5")
            {
                Console.WriteLine("\nGoodbye!");
                break;
            }
            
            // Get numbers
            double num1 = GetNumber("Enter first number: ");
            double num2 = GetNumber("Enter second number: ");
            
            // Perform calculation
            try
            {
                double result = 0;
                string operation = "";
                
                switch (choice)
                {
                    case "1":
                        result = calculator.Add(num1, num2);
                        operation = "+";
                        break;
                    case "2":
                        result = calculator.Subtract(num1, num2);
                        operation = "-";
                        break;
                    case "3":
                        result = calculator.Multiply(num1, num2);
                        operation = "*";
                        break;
                    case "4":
                        result = calculator.Divide(num1, num2);
                        operation = "/";
                        break;
                    default:
                        Console.WriteLine("Invalid choice!");
                        continue;
                }
                
                Console.WriteLine($"\nResult: {num1} {operation} {num2} = {result:F2}");
            }
            catch (DivideByZeroException ex)
            {
                Console.WriteLine($"\nError: {ex.Message}");
            }
            catch (Exception ex)
            {
                Console.WriteLine($"\nError: {ex.Message}");
            }
            
            Console.WriteLine("\nPress any key to continue...");
            Console.ReadKey();
        }
    }
    
    static double GetNumber(string prompt)
    {
        while (true)
        {
            Console.Write(prompt);
            if (double.TryParse(Console.ReadLine(), out double number))
                return number;
            Console.WriteLine("Invalid input! Please enter a number.");
        }
    }
}

Step 4: Enhanced Features

Add History Feature

List history = new List();

// After each calculation
string historyEntry = $"{num1} {operation} {num2} = {result:F2}";
history.Add(historyEntry);

// Display history option
Console.WriteLine("\nPress 'H' to view history");
if (Console.ReadKey().Key == ConsoleKey.H)
{
    Console.Clear();
    Console.WriteLine("=== HISTORY ===\n");
    if (history.Count == 0)
        Console.WriteLine("No calculations yet.");
    else
    {
        for (int i = 0; i < history.Count; i++)
            Console.WriteLine($"{i + 1}. {history[i]}");
    }
    Console.WriteLine("\nPress any key to continue...");
    Console.ReadKey();
}

Add Scientific Functions

public double Power(double a, double b) => Math.Pow(a, b);
public double SquareRoot(double a) => Math.Sqrt(a);
public double Sine(double a) => Math.Sin(a * Math.PI / 180);