The following code is for a programming class I'm taking. The program is supposed to prompt for a number, then prompt for a second number. Then it should use a while loop to multiply the first number by the second number. The second number does not change - the first number is continually multiplied until it equals 1000. Here's an example of what it should do:

enter 3
enter 3

3*3=9
9*3=27
27*3=81
81*3=243
243*3=729

And it should stop there. But, when I run the program I find that it continues to multiply up to some point - when I run the example of a=3, b=3, I get:

3*3=9
9*3=27
27*3=81
81*3=243
243*3=729
729*3=2187

How can I fix my code so it stops when either number reaches 1000?

#include <iostream.h>
#include <math.h>
#include <iomanip.h>

main()
{
    int num = 1;    
    long a;     
    long b;     
    long c;     
    
    cout<<"Welcome to the Multi-Loop Program.                    \n";
    cout<<"This program will prompt you to enter two numbers      \n";  
    cout<<"between 1 and 1000. It will then multiply the first   \n";
    cout<<"number by the second number up to or equal to 1000.   \n"<<endl;
    
    cout<<"To use the program, press 1. To exit, press 0. \n";   
    cout<<"Enter the number choice here. -> ";
    cin>>num;
    cout<<endl;

    while(num==1)
    {   
    a = 1;   
    b = 1;
    c = 1;                  
    cout<<"Enter the first number. (Between 1 and 1000) -> ";       
    cin>>a;                                                         
    cout<<endl;
    cout<<"Enter a number for the multiple. (Between 1 and 1000) -> ";
    cin>>b;
    cout<<endl;
    cout<<setw(10)<<a<<setw(10)<<a<<endl;           
		
    while(a >= 0 && a <= 1000 && b >= 1 && b <= 1000 && c >=0 && c <= 1000)
    {
         c = a * b;                                            
         cout<<setw(10)<<a<<"*"<<b<<"="<<setw(7)<<c<<endl;     
         a = c * b;                                            
         cout<<setw(10)<<c<<"*"<<b<<"="<<setw(7)<<a<<endl;     
    }                                                         
		                                                         
    cout<<endl;
    cout<<"Enter 1 to continue or 0 exit. -> ";         
    cin>>num;
    cout<<endl;
    }

	cout<<endl;
	cout<<"Thank you for using the Multi-Loop Program.";	

	return 0;
}
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