program to find prime number

Answer 1

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

#include <iostream>
using namespace std;

int main()
{
int n, i, flag=0;
cout << "Enter a positive integer: ";
cin >> n;
for(i=2;i<=n/2;++i)
{
if(n%i==0)
{
flag=1;
break;
}
}
if (flag==0)
cout << "This is a prime number";
else
cout << "This is not a prime number";
return 0;
}

Output

_________________________

Enter a positive integer: 29
This is a prime number.

_________________________
Enter a positive integer: 12
This is not a prime number.

Answer 2

https://code.sololearn.com/cWlQ6WzcAT1g

#include <iostream>
#include <math.h>
using namespace std;

bool isPrime(unsigned int n) {
unsigned int i;
double sqrtn;
if (n < 2) {
return false;
}
sqrtn = sqrt(n);
for (i = 2; i <= sqrtn; i++) {
if (n % i == 0) {
return false;
}
}
return true;
}

int main() {
unsigned int n;
cout << "Enter a number to check if it is prime: ";
cin >> n;
cout << n << endl;
cout << n << " is " << (isPrime(n)? "" : "not ") << "prime." << endl;
return 0;
}

And if you want to print the first prime numbers:
https://code.sololearn.com/cMoVkbtiyUu4