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.
If you don't know what is prime number please read for this tutorial. Prime Number & Prime Factors
Example
Input
Input any number: 10
Output
Prime factors of 10: 2, 5
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.
2 and 3 are the prime factors of 18.
Step by step descriptive logic to find prime factors.
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.
Print the value of i if it is prime and a factor of num.
/**
* 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 */
if(num%i==0)
{
/* Check 'i' for Prime */
isPrime = 1;
for(j=2; j<=i/2; j++)
{
if(i%j==0)
{
isPrime = 0;
break;
}
}
/* If 'i' is Prime number and factor of num */
if(isPrime==1)
{
printf("%d, ", i);
}
}
}
return 0;
}Enter any number to print Prime factors: 15
All Prime Factors of 15 are:
3, 5,
First read the algorithm, then study the program code line by line. After that, compare the code with the output and finally go through the explanation. This approach helps learners understand both the logic and the implementation properly.
After understanding this example, try to rewrite the same program without looking at the code. Then change some values or logic and run it again. This helps improve confidence and keeps learners engaged on the page for longer.