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Prime Factorization of a Number in C#

In this exercise, we will create a C# program that computes and displays the prime factorization of a user-provided number. Prime factorization is the process of breaking down a number into its smallest prime components. The program will repeatedly divide the number by its smallest prime factors until the quotient is 1. This exercise helps in understanding loops, number theory, and efficient factorization techniques in C#.



Group

C# Basic Data Types Overview

Objective

1. Prompt the user to enter an integer number.
2. Use a loop to find and extract the prime factors of the number.
3. Display the factors as a multiplication sequence.
4. Include `1` at the end of the factorization for consistency.
5. Ensure the program handles invalid or negative inputs gracefully.

Write a C# program that displays a number (entered by the user) as a product of its prime factors. For example, 60 = 2 · 2 · 3 · 5

Example C# Exercise

 Copy C# Code 
using System;

class Program
{
    static void Main()
    {
        // Ask the user for an integer input
        Console.Write("Enter a number: ");
        int number = Convert.ToInt32(Console.ReadLine());

        // Store the original number for output
        int originalNumber = number;

        // Start displaying the factorization
        Console.Write(originalNumber + " = ");

        // Find and print the prime factors
        bool firstFactor = true;

        // Divide by 2 while it's a factor
        while (number % 2 == 0)
        {
            Console.Write(firstFactor ? "2" : " · 2");
            number /= 2;
            firstFactor = false;
        }

        // Check odd numbers from 3 onwards
        for (int i = 3; i * i <= number; i += 2)
        {
            while (number % i == 0)
            {
                Console.Write(firstFactor ? i.ToString() : " · " + i);
                number /= i;
                firstFactor = false;
            }
        }

        // If a prime number remains (greater than 1), print it
        if (number > 1)
        {
            Console.Write(firstFactor ? number.ToString() : " · " + number);
        }

        // Append " · 1" for formatting consistency
        Console.WriteLine(" · 1");
    }
}

 Output

//Example 1: User enters 60
Enter a number: 60
60 = 2 · 2 · 3 · 5 · 1

//Example 2: User enters 84
Enter a number: 84
84 = 2 · 2 · 3 · 7 · 1

//Example 3: User enters 97 (a prime number)
Enter a number: 97
97 = 97 · 1

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More C# Practice Exercises of C# Basic Data Types Overview

Explore our set of C# Practice Exercises! Specifically designed for beginners, these exercises will help you develop a solid understanding of the basics of C#. From variables and data types to control structures and simple functions, each exercise is crafted to challenge you incrementally as you build confidence in coding in C#.