## In this Program, you’ll learn how to find Prime number entered by User.

**What is the prime number?**

To understand this example, you should have the knowledge of C programming :

A number is considered as the prime number when it satisfies the below conditions.

- It should be the whole number
- It should be greater than 1
- It should have only 2 factors. They are 1 and the number itself.

**Example for prime numbers:** 2, 3, 5, 7, 11, 13, 17, 19, 23 etc.

**Why 4, 6, 8, 9, 10, 12, 14, 15, 16 etc are not prime numbers?**

Because the number 4 can be factored as 2*2 and 1*4. As per the rule of prime number, there should be 2 factors only. They are 1 and the number itself. But, number 4 has 2*2 also. Like this, all remaining numbers 6, 8, 9, 10, 12, 14, 15, 16 have factors other than 1 and the number itself. So, these are not called as prime numbers.

#### Program to find Prime Numbers Entered by User

#include <stdio.h> int main() { int n, i, flag = 0; printf("Enter a positive integer: "); scanf("%d",&n); for(i=2; i<=n/2; ++i) { // condition for nonprime number if(n%i==0) { flag=1; break; } } if (flag==0) printf("%d is a prime number.",n); else printf("%d is not a prime number.",n); return 0; }

**Output****:**

Please enter a number: 13 Entered number is 13 and it is a prime number.

**Related C Programs**

- C program for factorial
- C program for Fibonacci series
- C Program to Print an Integer (Entered by the User)
- C Program to Add Two Integers

Ask your questions and clarify your/others doubts on C Prime Numbers by commenting.** Documentation**