- Write a C program to print all prime factors of a number.
- Wap in C to find all prime factors of given number.

#### Required Knowledge

- C printf and scanf functions
- For loop in C
- C Program to find factors of a number
- C program to check prime numbers

A **Prime Factor** of a number is a factor that is also a **prime number**.

A **Prime number** is a natural number greater than 1 that is only divisible by either 1 or itself.

For Example: Prime factors of 15 are 3 and 5.

## C program to print all prime factors of a number using for loop

#include <stdio.h> int main() { int counter, N, i, isPrime; printf("Enter a Number\n"); scanf("%d", &N); printf("List of Prime Factors of %d\n", N); /*Check for every number between 1 to N, whether it divides N */ for(counter = 2; counter <= N; counter++) { /* * If counter completely divides N, * then it is a factor of N */ if(N%counter==0) { /* Check if counter is also a prime number */ isPrime = 1; for(i = 2; i <=(counter/2); i++) { if(counter%i==0) { isPrime=0; break; } } if(isPrime==1) printf("%d ", counter); } } return 0; }

Output

Enter a Number 15 List of Prime Factors of 15 3 5

Enter a Number 50 List of Prime Factors of 50 2 5

**Write a C program to find product of digits of a number using while loop.**

Wap in C to multiply the digits of a number.

Wap in C to multiply the digits of a number.

#### Required Knowledge

To **multiply digits of a number** we have to remove one digit at a time, we can use '/' division and '%' modulus operator. Number%10 will give the least significant digit of the number, we will use it to get one digit of number at a time. To remove last least significant digit from number we will divide number by 10.

**Product of digits** of 2534 = 2 x 5 x 3 x 4 = 120

**Algorithm to find product of digits of a number**

- Get least significant digit of number (number%10) and multiply it to the product variable.
- Remove least significant digit form number (number = number/10).
- Repeat above two steps, till number is not equal to zero.

## C program to find sum of all even numbers between 1 to N using for loop

#include <stdio.h> #include <conio.h> int main() { int num, temp; long productOfDigit = 1; /* * Take a number as input from user */ printf("Enter a Number\n"); scanf("%d", &num); temp = num; while(num != 0){ /* get the least significant digit(last digit) of number and multiply it to productofDigit */ productOfDigit *= num % 10; /* remove least significant digit(last digit) form number */ num = num/10; } printf("Product of digits of %d = %ld", temp, productOfDigit); getch(); return 0; }

Output

Enter a Number 2436 Product of digits of 2436 = 144

Enter a Number 2222 Product of digits of 2436 = 16

**Related Topics**