Trinomial factoring

[Geralds mod]

I hate doing trinomials in class. The only way they taught us how to do them was guess and check.

(A trinomial looks like this: ax^2 + bx + c)
I made a C++ app that factors them into (x + )(x - ) form, and it also gives you the answers to X.

It only works with trinomials that look like this:
ax^2 + bx +c

Or ones that look like:
ax^2 + c

This kind doesn't work at this time:
ax^3 + bx + c

I would really appreciate it if someone could compile it and test a few trinomials in it. If there is a bug just say so. I might be able to fix it myself.

Trinomial factoring source code:

#include <iostream>
#include <string>
#include <stdio.h>
#include <cmath>
using namespace std;

double a, b, c, A, B, C, A2, ans1, ans2, ansgcd, q, t, x1, x2, answer;
char title[] = "Factor Trinomials";
char equation[] = "ax^2 + bx + c";	
char Exit = 'y';

void centerstring(char* string)
{
  int l = strlen(string);
  int pos = (int)((80 - l) / 2);
  for (int i = 0; i < pos; i++)
  	cout << " ";

  cout << string;
}
int gcd( int a, int b )
{
	c = 0;
    while(1)
    {
  		a = a % b;
		if( a == 0 )
			return b;
		b = b % a;
        if( b == 0 )
			return a;
    }
}

double square_root(double t)
{
	q = t / 2;
	while (1)
	{
		answer = 0.5*(q + (t / q));
		if (q == answer)
			return answer;
		q = answer;
	}
}

int main()
{
	while (Exit == 'y' || Exit == 'Y')
	{
		centerstring(title);
		cout << "\n";
		centerstring(equation);
		cout << "\nA = ";
		cin >> A;
		cout << "B = ";
		cin >> B;
		cout << "C = ";
		cin >> C;
		
			ans1 = B - square_root( (B * B) - (4 * A * C));
			ans2 = B + square_root( (B * B) - (4 * A * C));
			A = A * 2;
			A2 = A;
			ansgcd = gcd(A, ans1);
			if (ansgcd < 0)
			{
				A = A / -ansgcd;
				ans1 = ans1 / -ansgcd;
			}
			else
			{
				A = A / ansgcd;
				ans1 = ans1 / ansgcd;
			}		
			ansgcd = gcd(A2, ans2);
			if (ansgcd < 0)
			{
				A2 = A2 / -ansgcd;
				ans2 = ans2 / -ansgcd;
			}
			else
			{
				A2 = A2 / ansgcd;
				ans2 = ans2 / ansgcd;
			}
		
			cout << "\nAnswer is:\n("; 
			if (A == 1.0)
				cout << "x";
			else  
				cout << A << "x";
				
			if (ans1 < 0)
				cout << " - " << -ans1;
			else
				cout << " + " << ans1; 
		
			cout << ")(";
			if (A2 == 1.0)
				cout << "x";
			else  
				cout << A2 << "x";
				
			if (ans2 < 0)
				cout << " - " << -ans2;
			else
				cout << " + " << ans2;
		
			cout << ")";
			x1 = -ans1 / A;
			x2 = -ans2 / A2;
			cout << "\nX = " << x1 << " or " << x2;

			do 
			{
				cout << "\n\nFactor another? [y/n] ";
				cin >> Exit;
			} while (!Exit == 'n' && !Exit == 'N' && !Exit == 'y' && !Exit == 'Y');
			cout << "\x1b[2J\x1b[H" << flush;
	}
	return 0;
}

Thanks.

[magicalblender]

cmath conveniently has a its own square root function, which may be more accurate than yours. Try it out. It's called sqrt().

Near the end of your program, you write:

cout << "\x1b[2J\x1b[H" << flush;

What is the purpose of this line?

Other than that, this seems quite functional. Well done. :-)

EDIT: Found a bug- when a,b, and c equal zero, it hangs. I suspect the problem is with gcd().

[Geralds mod]

I made my own square root because sqrt was giving me problems. Something about it must be a double.

cout << "\x1b[2J\x1b[H" << flush;

That just clears the screen.

If your factoring a trinomial A,B and C will not equal 0.