Prime

/*
    Program in C to display all the prime factors of a given positive integer in descending order.
    Date : 6.01.2021
    Name : Shamba Chowdhury
    Roll no : 3135
*/

#include<stdio.h>
#include<stdlib.h>

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

    printf("Enter the number to find the Prime factors of : ");
    scanf("%d", &num);                      //Taking input of the number of which we have to find the prime factors

    if(num <= 0)
    {
        printf("Wrong input. Numbers less than or equal to 0 not allowed!");
        exit(0);
    }

    printf("\nAll the prime factors of %d in descending order are : \n", num);

    /*
        Outer loop to find the factors of the given number.
        The factors of a number can start from 2 and the factors are always less than half of the number
    */
    for(i = num/2; i >= 2; i--)
    {
        if(num % i == 0)
        {
            isPrime = 1;

            //Checking whether the factor is a prime or not
            for(j = 2; j <= i/2; j++)
            {
                if(i%j == 0)
                {
                    isPrime = 0;
                    break;
                }
            }

            //Printing the number if its a factor as well as prime
            if(isPrime == 1)
            {
                printf("%d ", i);
            }
        }
    }

    return 0;
}