C# Program to Find Factors of a Number

To find factors of a number in C#, use a for loop from 1 to the number and check if the number modulo the loop variable is zero with if (number % i == 0) to print the factor.

Examples

Input6

OutputFactors of 6 are: 1 2 3 6

Input13

OutputFactors of 13 are: 1 13

Input1

OutputFactors of 1 are: 1

How to Think About It

To find factors of a number, think about all numbers from 1 up to that number. For each, check if dividing the number by it leaves no remainder. If yes, that number is a factor because it divides evenly.

Algorithm

1

Get the input number from the user.

2

Start a loop from 1 to the input number.

3

For each number in the loop, check if the input number modulo this number is zero.

4

If yes, print this number as a factor.

5

End the loop after reaching the input number.

Code

csharp

using System;
class Program {
    static void Main() {
        Console.Write("Enter a number: ");
        int number = int.Parse(Console.ReadLine());
        Console.Write($"Factors of {number} are: ");
        for (int i = 1; i <= number; i++) {
            if (number % i == 0) {
                Console.Write(i + " ");
            }
        }
    }
}

Output

Enter a number: 6
Factors of 6 are: 1 2 3 6 

Dry Run

Let's trace the input 6 through the code to find its factors.

1

Input number

User enters 6, so number = 6

2

Start loop

Loop i from 1 to 6

3

Check i=1

6 % 1 == 0, so print 1

4

Check i=2

6 % 2 == 0, so print 2

5

Check i=3

6 % 3 == 0, so print 3

6

Check i=4

6 % 4 != 0, skip

7

Check i=5

6 % 5 != 0, skip

8

Check i=6

6 % 6 == 0, so print 6

i	number % i	Is factor?
1	0	Yes
2	0	Yes
3	0	Yes
4	2	No
5	1	No
6	0	Yes

Why This Works

Step 1: Loop through numbers

We check every number from 1 to the input number to see if it divides evenly.

Step 2: Use modulo operator

The % operator gives the remainder. If remainder is zero, it means the number divides evenly.

Step 3: Print factors

When a number divides evenly, we print it as a factor.

Alternative Approaches

Check factors up to square root

csharp

using System;
class Program {
    static void Main() {
        Console.Write("Enter a number: ");
        int number = int.Parse(Console.ReadLine());
        Console.Write($"Factors of {number} are: ");
        for (int i = 1; i * i <= number; i++) {
            if (number % i == 0) {
                Console.Write(i + " ");
                if (i != number / i) {
                    Console.Write((number / i) + " ");
                }
            }
        }
    }
}

This method is faster for large numbers because it only checks up to the square root, but factors may print in no particular order.

Using List to store factors

csharp

using System;
using System.Collections.Generic;
class Program {
    static void Main() {
        Console.Write("Enter a number: ");
        int number = int.Parse(Console.ReadLine());
        List<int> factors = new List<int>();
        for (int i = 1; i <= number; i++) {
            if (number % i == 0) {
                factors.Add(i);
            }
        }
        Console.WriteLine($"Factors of {number} are: {string.Join(" ", factors)}");
    }
}

This approach collects factors first, which can be useful if you want to use them later, but uses extra memory.

Complexity: O(n) time, O(1) space

Time Complexity

The program checks every number from 1 to n, so it runs in linear time O(n).

Space Complexity

It uses constant extra space O(1) since it prints factors directly without storing them.

Which Approach is Fastest?

Checking up to the square root of n is faster (O(√n)) but more complex to implement and may print factors unordered.

Approach	Time	Space	Best For
Check all numbers 1 to n	O(n)	O(1)	Simplicity and small numbers
Check up to square root	O(√n)	O(1)	Large numbers and performance
Store factors in list	O(n)	O(n)	When factors need reuse or sorting