Thread: odd error

your prime function is expecting a pointer to a variable and you are simply only passing a variable:

try something like:

Code:

 else if( choice == 1 )
   {
      long unsigned int num;
      
      cout << "\nEnter number: ";
      cin >> num;
   
      if ( prime( &num ) == 1 )
         cout << "The number is prime.";
      else
         cout << "The number is NOT prime."; 
   }


int prime( int &number )
{
...
}

I was not using pointers. Your example also displays an error. The error only happens with a long unsigned int. With a normal int everything works fine.

test.cpp: In function `int main()':
test.cpp:39: error: could not convert `&num' to `int&'
test.cpp:5: error: in passing argument 1 of `int prime(int&)'

Performance wise, is it worth using pass-by-reference?

[EDIT]

By changing the function to

Code:

int prime( long unsigned int &number )
{
...
}

The error is resolved. I still would like to know if there is a performance gain by using references?

how about this:

Code:

int prime (unsigned long int & number) {

        . . . 
}

make sure you variable types are the same.

edit: performance wise if you are dealing with very large numbers than, yes it is preferable to use pass by reference.