C program to find prime factors of a number

Write a C program to input a number from user and find Prime factors of the given number using loop. C program to list all prime factors of a given number. Logic to find prime factors of a number in C programming.



Input any number: 10


Prime factors of 10: 2, 5

Required knowledge

Basic C programming, If statement, For loop, Nested loop

What is Prime factor?

Factors of a number that are prime numbers are called as Prime factors of that number. For example: 2 and 5 are the prime factors of 10.

Logic to check prime factors of a number

Step by step descriptive logic to find prime factors.

  1. Input a number from user. Store it in some variable say num.
  2. Run a loop from 2 to num/2, increment 1 in each iteration. The loop structure should look like for(i=2; i<=num/2; i++).

    You may think why loop from 2 to num/2? Because prime number starts from 2 and any factor of a number n is always less than n/2.

  3. Inside the loop, first check if i is a factor of num or not. If it is a factor then check it is prime or not.

    Print the value of i if it is prime and a factor of num.

Program to find prime factors of a number

 * C program to find all prime factors of a given number

#include <stdio.h>

int main()
    int i, j, num, isPrime;

    /* Input a number from user */
    printf("Enter any number to print Prime factors: ");
    scanf("%d", &num);

    printf("All Prime Factors of %d are: \n", num);

    /* Find all Prime factors */
    for(i=2; i<=num; i++)
        /* Check 'i' for factor of num */
            /* Check 'i' for Prime */
            isPrime = 1;
            for(j=2; j<=i/2; j++)
                    isPrime = 0;

            /* If 'i' is Prime number and factor of num */
                printf("%d, ", i);

    return 0;


Enter any number to print Prime factors: 15
All Prime Factors of 15 are: 
3, 5,

Happy coding 😉

About Pankaj

Pankaj Prakash is the founder, editor and blogger at Codeforwin. He loves to learn new techs and write programming articles especially for beginners. He works at Vasudhaika Software Sols. as a Software Design Engineer and manages Codeforwin. In short Pankaj is Web developer, Blogger, Learner, Tech and Music lover.

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