Basic calculator program using C#

A calculator program in C# can be built using either Windows Forms or Console applications. This tutorial demonstrates how to create a basic calculator that performs fundamental arithmetic operations like addition, subtraction, multiplication, and division.

We'll create a complete console-based calculator that takes user input and performs calculations, making it easy to understand the core logic before moving to GUI implementations.

Console-Based Calculator

Basic Calculator with Menu

using System;

class Calculator {
    public static void Main(string[] args) {
        double num1, num2, result;
        char operation;
        
        Console.WriteLine("=== Basic Calculator ===");
        Console.WriteLine("Enter first number: ");
        num1 = 10.5; // Simulating user input
        Console.WriteLine("10.5");
        
        Console.WriteLine("Enter operation (+, -, *, /): ");
        operation = '+'; // Simulating user input
        Console.WriteLine("+");
        
        Console.WriteLine("Enter second number: ");
        num2 = 5.2; // Simulating user input
        Console.WriteLine("5.2");
        
        switch (operation) {
            case '+':
                result = num1 + num2;
                Console.WriteLine($"{num1} + {num2} = {result}");
                break;
            case '-':
                result = num1 - num2;
                Console.WriteLine($"{num1} - {num2} = {result}");
                break;
            case '*':
                result = num1 * num2;
                Console.WriteLine($"{num1} * {num2} = {result}");
                break;
            case '/':
                if (num2 != 0) {
                    result = num1 / num2;
                    Console.WriteLine($"{num1} / {num2} = {result}");
                } else {
                    Console.WriteLine("Error: Division by zero!");
                }
                break;
            default:
                Console.WriteLine("Invalid operation!");
                break;
        }
    }
}

The output of the above code is −

=== Basic Calculator ===
Enter first number: 
10.5
Enter operation (+, -, *, /): 
+
Enter second number: 
5.2
10.5 + 5.2 = 15.7

Object-Oriented Calculator

Calculator Class with Methods

using System;

class Calculator {
    public double Add(double a, double b) {
        return a + b;
    }
    
    public double Subtract(double a, double b) {
        return a - b;
    }
    
    public double Multiply(double a, double b) {
        return a * b;
    }
    
    public double Divide(double a, double b) {
        if (b == 0) {
            throw new DivideByZeroException("Cannot divide by zero!");
        }
        return a / b;
    }
    
    public double Power(double baseNum, double exponent) {
        return Math.Pow(baseNum, exponent);
    }
    
    public double SquareRoot(double number) {
        if (number < 0) {
            throw new ArgumentException("Cannot calculate square root of negative number!");
        }
        return Math.Sqrt(number);
    }
}

class Program {
    public static void Main(string[] args) {
        Calculator calc = new Calculator();
        
        Console.WriteLine("=== Calculator Operations ===");
        Console.WriteLine("Addition: " + calc.Add(15, 25));
        Console.WriteLine("Subtraction: " + calc.Subtract(50, 30));
        Console.WriteLine("Multiplication: " + calc.Multiply(6, 7));
        Console.WriteLine("Division: " + calc.Divide(100, 4));
        Console.WriteLine("Power: " + calc.Power(2, 3));
        Console.WriteLine("Square Root: " + calc.SquareRoot(64));
        
        // Demonstrating error handling
        try {
            Console.WriteLine("Division by zero: " + calc.Divide(10, 0));
        } catch (DivideByZeroException ex) {
            Console.WriteLine("Error: " + ex.Message);
        }
    }
}

The output of the above code is −

=== Calculator Operations ===
Addition: 40
Subtraction: 20
Multiplication: 42
Division: 25
Power: 8
Square Root: 8
Error: Cannot divide by zero!

Windows Forms Calculator Structure

For GUI-based calculators using Windows Forms, the basic structure involves button click events. Here's the corrected approach for handling operations −

public partial class Calculator : Form {
    private double firstNumber = 0;
    private double secondNumber = 0;
    private char operation;
    private bool operationPressed = false;
    
    private void btnAdd_Click(object sender, EventArgs e) {
        firstNumber = Convert.ToDouble(txtResult.Text);
        operation = '+';
        operationPressed = true;
        txtResult.Clear();
    }
    
    private void btnEquals_Click(object sender, EventArgs e) {
        secondNumber = Convert.ToDouble(txtResult.Text);
        double result = 0;
        
        switch (operation) {
            case '+': result = firstNumber + secondNumber; break;
            case '-': result = firstNumber - secondNumber; break;
            case '*': result = firstNumber * secondNumber; break;
            case '/': 
                if (secondNumber != 0)
                    result = firstNumber / secondNumber;
                else {
                    txtResult.Text = "Error";
                    return;
                }
                break;
        }
        
        txtResult.Text = result.ToString();
        operationPressed = false;
    }
}

Advanced Calculator with Multiple Operations

using System;

class AdvancedCalculator {
    public static double Calculate(double num1, double num2, string operation) {
        switch (operation.ToLower()) {
            case "add":
            case "+":
                return num1 + num2;
            case "subtract":
            case "-":
                return num1 - num2;
            case "multiply":
            case "*":
                return num1 * num2;
            case "divide":
            case "/":
                return num2 != 0 ? num1 / num2 : throw new DivideByZeroException();
            case "modulo":
            case "%":
                return num1 % num2;
            default:
                throw new ArgumentException("Invalid operation");
        }
    }
    
    public static void Main(string[] args) {
        double a = 20, b = 8;
        
        Console.WriteLine("=== Advanced Calculator ===");
        Console.WriteLine($"Numbers: {a}, {b}");
        Console.WriteLine();
        
        string[] operations = { "+", "-", "*", "/", "%" };
        string[] names = { "Addition", "Subtraction", "Multiplication", "Division", "Modulo" };
        
        for (int i = 0; i < operations.Length; i++) {
            try {
                double result = Calculate(a, b, operations[i]);
                Console.WriteLine($"{names[i]}: {a} {operations[i]} {b} = {result}");
            } catch (DivideByZeroException) {
                Console.WriteLine($"{names[i]}: Error - Division by zero");
            }
        }
        
        // Scientific operations
        Console.WriteLine($"Power: {a}^3 = {Math.Pow(a, 3)}");
        Console.WriteLine($"Square Root: ?{a} = {Math.Sqrt(a):F2}");
        Console.WriteLine($"Absolute: |{-a}| = {Math.Abs(-a)}");
    }
}

The output of the above code is −

=== Advanced Calculator ===
Numbers: 20, 8

Addition: 20 + 8 = 28
Subtraction: 20 - 8 = 12
Multiplication: 20 * 8 = 160
Division: 20 / 8 = 2.5
Modulo: 20 % 8 = 4
Power: 20^3 = 8000
Square Root: ?20 = 4.47
Absolute: |-20| = 20

Key Features of Calculator Programs

• Error Handling: Always check for division by zero and invalid inputs.

• Data Types: Use double for decimal calculations instead of int.

• User Interface: Provide clear prompts and formatted output.

• Validation: Validate user input before performing calculations.

• Extensibility: Design the calculator to easily add new operations.

Conclusion

Building a calculator program in C# involves understanding basic arithmetic operations, error handling, and user interface design. Whether using console applications or Windows Forms, the core logic remains the same: capture input, perform calculations, and display results with proper error handling for edge cases like division by zero.