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.

**Example**

**Input**

Input any number: 10

**Output**

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.

- Input a number from user. Store it in some variable say
`num`. - 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`

. - 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 */
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;
}
```

Output

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

Happy coding 😉

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