﻿ # Prime

Jan 7th, 2021
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1. /*
2.     Program in C to display all the prime factors of a given positive integer in descending order.
3.     Date : 6.01.2021
4.     Name : Shamba Chowdhury
5.     Roll no : 3135
6. */
7.
8. #include<stdio.h>
9. #include<stdlib.h>
10.
11. int main()
12. {
13.     int i, j, num;
14.     int isPrime;
15.
16.     printf("Enter the number to find the Prime factors of : ");
17.     scanf("%d", &num);                      //Taking input of the number of which we have to find the prime factors
18.
19.     if(num <= 0)
20.     {
21.         printf("Wrong input. Numbers less than or equal to 0 not allowed!");
22.         exit(0);
23.     }
24.
25.     printf("\nAll the prime factors of %d in descending order are : \n", num);
26.
27.     /*
28.         Outer loop to find the factors of the given number.
29.         The factors of a number can start from 2 and the factors are always less than half of the number
30.     */
31.     for(i = num/2; i >= 2; i--)
32.     {
33.         if(num % i == 0)
34.         {
35.             isPrime = 1;
36.
37.             //Checking whether the factor is a prime or not
38.             for(j = 2; j <= i/2; j++)
39.             {
40.                 if(i%j == 0)
41.                 {
42.                     isPrime = 0;
43.                     break;
44.                 }
45.             }
46.
47.             //Printing the number if its a factor as well as prime
48.             if(isPrime == 1)
49.             {
50.                 printf("%d ", i);
51.             }
52.         }
53.     }
54.
55.     return 0;
56. }
57.
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