C++, PRogram homework, need a doublecheck

Hey all. Simple program for homework, find all the Primes then figure out which ones are twins <come one after another>
its works but just wanted to see if anyone can spot any logical erros that migth crop up

Code:

/* Due Date:             February ??, 2004
   Software Designer:    Stephen Fritz
   Course:               420-DBF
   Deliverable:          Assignment 1, Flow logic.
   Description:          This program takes two numbers
                         as input, and calculates all
                         prime numbers in between
                         those two numbers.
  Version:               3
*/



#include <iostream>

using std::cout;

bool CheckPrime(unsigned long);

/*************************************************
Takes the Start and End, runs threw all the numbers
between them, finds out the primes, stores them in
the array and then size the number of primes back to main
***************************************************/
void CalcPrimes(unsigned long start, unsigned long end, unsigned long *PrimeArray, unsigned long *size) {


    long unsigned pos = 0;
    for( unsigned long x = start; x <= end; x += 2) {

         if(CheckPrime(x)) {
               *PrimeArray = x;

               pos++;
               PrimeArray++;
               }
       }

       *size = pos - 1;
      return;
     }

/******************
Checks numbers to
see if they are
prime or not
****************/

bool CheckPrime(unsigned long Pnum) {

     int x  = 3;

     if( Pnum % 2 == 0) // if number divisible by 2, its not prime
     return false;

     else {
      while (x < (Pnum)) {
        if(Pnum % x == 0) // number divisible by x? if so then no prime
                return false;
        x += 2;
        }
        }
     return true; // if i get here then its prime
}


/***************************************
Function Simply checks if two
numbers are two apart. if so,
they are twins. Must only be given primes
*****************************************/

bool TwinPrime(unsigned long x, unsigned long y) { // x must come first
     if ( (x + 2) == y)
        return true;
     else
         return false;

    }






/**********************************
Main. Takes two digits as input.
Finds all primes between those numbers
Inclusivly. Then takes those primes
and finds out which ones are Pairs
and prints out a list
*********************************/


int main(int argc, char *argv[])
{
  unsigned long start, end, temp, size;
  size =0;
  cout<<"Please input enter the range from the numbers you wish to input\n";
  cin>>start;
  cin>>end;

  if (start > end) { // If the numbers are put in out of order, switch them.
  temp = start;
  start = end;
  end = temp;
  }
  size = end - start;

  unsigned long *primes = new unsigned long[size];


  // Find those primes
  CalcPrimes(start, end, primes, &size);

  temp = 0;
  unsigned long TempX, TempY;
  cout<<"List of twin primes\n";
 //Printing the List of Twin Primes

  while ( temp != size) {
  TempX = primes[temp];
  TempY = primes[temp + 1];
  if (TwinPrime(TempX, TempY))

     cout<<TempX<<","<<TempY<<endl;
    temp++;
  }


  cin>>temp;
  return 0;
}

 

Dont know if this happend with you(or even matters), but it seems that unless the first number the user enters is prime you get a error. I tried a few for example:
11, 70 (worked fine)
10, 70 (got an error)
2, 61 (got an error)
1, 61 (worked fine)
If you already knew about this oops on my part... but just incase thought I would write something...

 

Thanks, i'd forgotten about this
I figure that out to be and eror in my logic. Which was easy to fix. Thanks for input

Friend had found it other day. the problem was that i was taking start, and adding two too it to cycle threw all odd numbers, which would have worked fine, accept when start is even, so i'm only cycling threw even numbers

 

glad to be of help...