if (argc == 3)
   {
 
   }

#include <cstdlib>
#include <iostream>
#include <iomanip>
#include <stdlib.h>
 
using namespace std;
const unsigned W = 10;
 
int main(int argc, char *argv[])
{
   const unsigned long arraySize = 1000000;
   bool a[arraySize];
   unsigned long num1;
   unsigned long num2;
   unsigned long num3;
   unsigned long counter = 0;
   unsigned long primes = 0;
   char z;
   unsigned long answer = 0;
 
//Initializing elements to 1 
 
for (int i = 0; i < arraySize; i++)             
{
   a[i] = 1;
}       
// For array subscript 2, all elements beyond 2 in the array that
// are multiples of 2 will be set to zero; for array subscript 3, 
// all elements beyond 3 in the array that 
// are multiples of 3 will be set to zero
 
 
for (int i = 2; i * i < arraySize; i++)
{
    if (a[i])
       for (int j = i + i; j < arraySize; j += i)
          a[j] = 0;
} 
// if user enters more than 3 numbers or 0 numbers
// program should output useful information
// and title and author
 
if ((argc > 4) || (argc == 1))
{
cout<<"This is Programming Assignment #5"<<endl;
cout<<"THE SIEVE OF ERATOSTHENES"<<endl;
cout<<"by Jeremy Rice"<<endl;
cout<<endl;
cout<<"Usage:"<<endl;
cout<<"\tprime num1 - determines if num1 is a prime"<<endl;
cout<<"\tprime num1 num2 - displays primes between numbers."<<endl;
}
 
 
 
num1 = atoi(argv[1]);
num2 = atoi(argv[2]);
num3 = num1;
// if user enters one number
// program should determine if that number is a prime
 
if ((argc > 1) && (argc < 3))
{
   if (a[num1] == 1)
   cout<<num1<<" is a prime number."<<endl;
   else
   cout<<num1<<" is not a prime number."<<endl;
}
 
// if user enters 2 numbers
// program, should calculate the prime numbers 
// between the two numbers
 
if (argc == 3) 
   for (int i = num1; num1 < num2; num1++)
 
    if (num1 < num2)
    if (a[num1] == 1)
     {
      counter++; 
      cout<<setw(W)<<num1;
     }
       else if
        (a[num1] == 0)
     {
         cout<<"";
     }   
        else 
          cout<<"num1 must be lower than num2."<<endl;          
if (num1 > num2)
{
cout<<"Error: Invalid user specified number."<<endl;
return 0;
}
cout<<endl;
cout<<"There are "<<counter<<" primes between "<<num3<<" and "<<num1<<endl;
return EXIT_SUCCESS;
}