C# Exercise: 133 Function Multiply & MultiplyR

// Import the System namespace to use basic classes like Console
using System;

class Program
{
    // Function to multiply two numbers iteratively using addition
    public static int Multiply(int a, int b)
    {
        int product = 0;  // Variable to store the product

        // Add 'a' to itself 'b' times to simulate multiplication
        for (int i = 0; i < Math.Abs(b); i++)
        {
            product += a;  // Add 'a' repeatedly
        }

        // If b is negative, the product should be negative
        if (b < 0)
        {
            product = -product;  // Negate the product
        }

        return product;
    }

    // Function to multiply two numbers recursively using addition
    public static int MultiplyR(int a, int b)
    {
        // Base case: if b is 0, the product is 0
        if (b == 0)
        {
            return 0;
        }
        else
        {
            // Recursive case: add 'a' recursively and handle negative b
            if (b < 0)
            {
                return -a + MultiplyR(a, b + 1);  // For negative b, subtract 'a'
            }
            else
            {
                return a + MultiplyR(a, b - 1);  // For positive b, add 'a'
            }
        }
    }

    // Main function to test the Multiply and MultiplyR functions
    public static void Main()
    {
        // Test the Multiply function
        Console.WriteLine("Iterative Multiply:");
        Console.WriteLine("3 * 4 = " + Multiply(3, 4));  // Expected output: 12
        Console.WriteLine("-3 * 4 = " + Multiply(-3, 4));  // Expected output: -12
        Console.WriteLine("3 * -4 = " + Multiply(3, -4));  // Expected output: -12
        Console.WriteLine("0 * 4 = " + Multiply(0, 4));  // Expected output: 0

        // Test the MultiplyR function
        Console.WriteLine("\nRecursive Multiply:");
        Console.WriteLine("3 * 4 = " + MultiplyR(3, 4));  // Expected output: 12
        Console.WriteLine("-3 * 4 = " + MultiplyR(-3, 4));  // Expected output: -12
        Console.WriteLine("3 * -4 = " + MultiplyR(3, -4));  // Expected output: -12
        Console.WriteLine("0 * 4 = " + MultiplyR(0, 4));  // Expected output: 0
    }
}