# Check whether Given Number is Prime Number or Not

Check whether Given Number is Prime Number or Not” is again very basic problem of programming exercise. Here, we are given a number, entered by user and our task is to check whether entered number is prime number or not.

Prime Number: A number is said to be prime number if it is only divisible by 1 and by itself.

Examples of Prime numbers are 2,3,5,7,11,…

NOTE: 1 is not a prime number.

Example:

```INPUT:
Number = 7
OUTPUT:
7 is a prime number.
INPUT:
Number = 9
OUTPUT:
9 is not a prime number.```

To check whether a number is prime number or not, we will check whether entered number is divisible from numbers 2 to (number-1). If any number from that range is divisible by entered number, then it is not a prime number. Else, it is a prime number.

C++ Program to check whether a number is prime number or not is as follows:

```#include<bits/stdc++.h>
using namespace std;
int main()
{
int num;

//Scan the number
cout<<"Enter the number:";
cin>>num;

bool res = true;
/*
We will check whether entered number is
divisible by numbers from 2 to (num-1).
If entered number is divisible by any number
from 2 to (num-1), then it is not prime number.
Else, it is prime number.
*/
for(int i = 2 ; i < num ; i++)
{
if(num % i == 0)
{
res = false;
break;
}
}

if(res == true && num!=1) /* 1 is not a prime number */
cout<<num<<" is a prime number";
else
cout<<num<<" is not a prime number";
}

```
```OUTPUT:
Enter the number: 11
11 is a prime number```

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