findthenextprime.cpp

#include <iostream>
#include <math.h>
using namespace std;
// declare functions
int prime(int n);

int main() {
    int n1;
    int i;
    bool isprime;
    
    cout << "enter a number to test for first prime above ";
    cin >> n1;
    
    for(i = n1; !isprime; i++) {
        isprime = prime(i);
    }
    cout << i << " is the next greatest prime" << endl;
    
    return 0;
}

int prime(int n) {
    int i;
    int sn;
    
    sn = sqrt((double)n);
    for(i=2; i<=sn; i++) {
        if(n%i==0)
            return false;
    }
    return true;
}