need immediate help pls?

[jaymz]

im doing a console program.
can you figure out what's wrong with this code??
how can i make it re-execute the program at runtime.

the program prompts the user to assign a value for x.
x should be less than m. where m = 8.
when the input is greater than m.
the program the program will prompt for another value that shuold be less than m.
here's the formula.
x = (x*a+c)mod m

it's involves recursion.
when f is already equal to x. recursion stops.


here's the code:(it's not yet finished.)

#include <iostream>

using std::cout;
using std::cin;
using std::endl;


void generate(int x)
{
	int m, a, c, p1, p2, f, n, d;

	m = 8;
	if (x < m)
	{
	a = 5;
	c = 7;

	p1 = x * a;
	p2 = p1 + c;
	f = p2 % m;
	n = 0;

	printf("\t%d\t%d\t%d\t%d\t%d\t\n",n,x,p1,p2,f);

		do
		{
		d = f;
		p1 = d * a;
		p2 = p1 + c;
		f = p2 % m;
		n = n++;

		printf("\t%d\t%d\t%d\t%d\t%d\t\n",n,d,p1,p2,f);
		}while(x <= f);
	}
	else
	{
		cout<<"x should be less than m";
	}

}

void main()
{
	int x;

	cout<< "Assign Value for x: ";

	cin>> x;

	printf("\tn\tx\tp1\tp2\tf\n\n");

	generate(x);
}

thanks.

[muzhogg]

Hi Jaymz,

There are a few basic problems with the code (although probably NOT the problems that you actually want us to help with!)

First is that void main() is non-standard C++ and you really SHOULD be using int main() (or even preferably int main(int argc, char *argv[])). In which case you need to include return 0; in main().

Second, there are none of those lovely comments which are supposed to be there to help other people make sense of what you're trying to do.

Third, you've got a curious mix of C and C++ code in there -- why precisely are you using both cout and printf()?

May I suggest that you fix these and see if it doesn't help? This may seem pointless, but believe me when I say if you insert CLEAR comments which indicate when you are entering a loop, checking an exit condition, etc, then you will see your problem -- a quick look at the section of the function generate(x) below should serve to demonstrate both why your program isn't working as you want AND the advantage of clear commenting;

        int m, a, c, p1, p2, f, n, d;

	m = 8;

        // if else loop
        // proceeds if (x<m), else prints error message and exits generate(x)   
	if (x < m)       
	{
	a = 5;
	c = 7;

But you don't WANT to exit if (x<m) is false, right?

For what it's worth -- I usually start small programs like this by writing comments explaining what I'm trying to achieve;

        // prompt user for an input. if input is out of range, prompt again (need
        // an exit condition, though). if input is within range, then perform
        // calculation

        // top of input loop - use cin to get input, use "q" as exit condition 
        // both "q" and valid input will terminate loop - but only valid input
        // will call the calculation 
        
             // if input valid perform calculation (and terminate loop)

             // if input invalid show error message

             // if input "q" do nothing (and terminate loop)

        // bottom of input loop

        // And so on...

All I then need to do is slip in the relevant code under each heading.

Hope it helps in more than one way!

Regards,
muzhogg