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# In this chapter of C++ program tutorial out task is:

• Write a c++ program to check whether a number is prime or not.

### C++ program to check a number is prime or not

Below is the C++ program to check a number is prime or not.

``````/*  Program Name : To check whether a number is prime or not
Program Author : Sayantan Bose
*/
#include<iostream>

//math.h header file is used for the sqrt function

#include<math.h>
using namespace std;

//This is function that check whether a number is prime or not
//This is the function that returns true if it is prime or return false if it is not a prime number

bool isPrime(int number)
{
int factor;
if(number == 0 || number == 1)
return false;
for(factor=2;factor<sqrt(number);factor++)
{
if(number % factor == 0){
return false;
break;
}
}
return true;
}

//This is the main function

int main()
{
int number,IsPrime;
cout<<"Enter the number to check prime or not: "<<endl;
cin>>number;
IsPrime = isPrime(number);
if(IsPrime)
cout<<number<<" : is a prime number"<<endl;
else
cout<<number<<" : is not a prime number"<<endl;
return 0;
}
``````

# OUTPUT :

Enter the number to check prime or not:

17
17 : is a prime number

EXPLANATION :
In the above c++ program to check if a number is prime:
• In the function isPrime has a return type bool i.e. either it will return true or false.
• Then inside the function it is checked whether the number is divided by any factor other than the number itself and 1.
• If the number is divided by the number itself or by 1 then the function return the true result else return false.
• According to the value returned by the isPrime function the following statement is executed in main function.

You can see the above code execution and output in codeblocks IDE: CPP Programs

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