# C++ Program to check whether a Number is Prime or not

## To check if a number is prime or not in C++

Here , in this section we will discuss  a program to check if a number is prime or not in C++. A number is said to be Prime Number if and only if it is divisible by one and itself.

• Sample test case 1 :
Input : 12
Output :The given number is not a prime number.
Explanation : As 12 is divisible by 1, 2,  3, 4, 6 and 12 so, it is not a prime number.

• Sample test case 2 :
Input : 23
Output :The given number is a prime number.
Explanation : 23 is divisible by 1 and 23, so it is a prime number.

## Algorithm :

• Take the number from the user and store it in variable n.
• Initialize the variable flag with value 0.
• Run a loop from 2 to sqrt(n)
• Check for every value if n is divisible by any number then set flag =1 and break the loop.
• If flag = 0 then print the given number is prime.
• Else print the number is not prime.

## C++ Program based on above algorithm

`#include<bits/stdc++.h>using namespace std;int main () {  int n, flag = 0;    cout << "Enter the number to check if it is prime or not: ";  cin >> n;    for (int i = 2; i <= sqrt (n); i++)    {      if (n % i == 0){	    flag = 1;	    break;	  }    }    if (flag == 0)    cout << "The given number is prime";  else    cout << "The given number is not prime";    return 0;}`
`Output :Enter the number to check if it is prime or not: 23The given number is prime`