I am working my way through the C++ without fear new edition, and have found some codes that dont work. This is a simple code to work out if a number is prime using the square root function and modulus. Here is the code as per the book:

Code:
```#include <iostream>
#include <cmath>

using namespace std;

int main()

{
int n;
int i;
int isPrime = true;

cout << "Please enter a number and press enter " ;
cin >> n;
cout << endl;

i = 2;

while (i <= sqrt(double(n)))// or (i*i<=n)
{
if (n % i == 0)

isPrime = false;
i++;
}

if (isPrime)

cout << "Number is a prime number" << endl;

else

cout << "Number is not a prime number" << endl;

}```
The word double which is in red, is what I had to add to get past the errors stating that the compile was unsure if it was supposed to return a float double etc.

Now the next part of the exercise was to take the square root function out of the loop, and declare a new variable as the result of the square root of the users input, then get the function to check it if was a prime number, here is how far I got

Code:
```#include <iostream>
#include <cmath>

using namespace std;

int main()

{
float m;
int n;
int i = 2;
int isPrime = true;

cout << "Please enter a number and press enter " ;
cin >> n;
cout << endl;

m = sqrt (float (n));

cout << m;
cout << endl;

while (i <= m ) // or (i*i<=n)
{
if (m % i == 0)

isPrime = false;
break;
}
i++;

if (isPrime)

cout << "Number is a prime number" << endl;

else

cout << "Number is not a prime number" << endl;

}```
I now get the error message error C2296: '%' : illegal, left operand has type 'float'. So how do I now complete this exercise, taking into account I am only on chapter 2 of the book

Last edited by shabbir; 11Aug2011 at 13:26.. Reason: Code blocks