Help Foiling

[ascii]

Hey! I've been working on making a program to foil two sets of numbers. If you don't remember from Algebra 1 xD, foiling is used to multiply two binomials, and stands for:
First
Outer
Inner
Last

I have the main part of the program done, but for some reason it keeps getting caught at index 7. Please help me out here!

#include<iostream>
using std::cout;
using std::cin;
using std::endl;

const int max = 30;

class CFoil
{  
public:
	CFoil(char* pequ);		// constructor				
	void foil();			// foil
private:
	int coefficient1, coefficient2, number1, number2;
	bool co1, co2, num1, num2;
	int index;
	char* str;

	void evaluate();		// evaluate the equation and output it
};

CFoil::CFoil(char* pequ):
	co1(true), co2(false), num1(true), num2(false), index(0), coefficient1(0), coefficient2(0), number1(0), number2(0)
{
	str = &(*pequ);			// make str point to the address of the value pointed to by pequ
}

void CFoil::foil()
{
	for(;;)
	{
		cout << index << endl;
		switch(*(str+index++))
		{
		case '(':
			if(*(str+index) == 'x')
			{
				if(co1)
				{
					coefficient1 = 1;
					co1 = false;
					co2 = true;
					break;
				}
				if(co2)
					coefficient2 = 1;
			}
			
			while(*(str + index) != 'x')
			{		   
				if(co1)
				{
					coefficient1 *= 10;
					coefficient1 += *(str+index++) - '0';
				}
			}

			co1 = false;
			co2 = true;
			break;

		case '+':	
			while(*(str+index) != ')')
			{
				number1 *= 10;
				number1 += *(str+index++) - '0';
			}
			
			num1 = false;
			num2 = true;
			break;

		case '-':
			while(*(str+index) != ')')
			{
				number1 *= 10;
				number1 -= *(str+index++) - '0';
			}
			
			num1 = false;
			num2 = true;
			break;

		case '\0':
			this->evaluate();
			break;
		}
	}
}

void CFoil::evaluate()
{
	int first = coefficient1 * coefficient2;
	int outer = coefficient1 * number2;
	int inner = coefficient2 * number1;
	int last = number1 * number2;

	cout << "\t\t\t=" << first << "+" << outer + inner << "+" << last
		<< endl;
	
	return;
}

int main(void)
{
	char equation[max] = "(3x+2)(5x-1)";	  
	char* pequation = equation;
	
	CFoil solve(pequation);
	solve.foil();

	cout << endl;
	return 0;
}

[helios]

Wouldn't it have been much easier to parse "3 2 5 -1" than "(3x+2)(5x-1)"? Your code breaks if I try to get even a little bit creative with the expression. E.g. "(x/5--1)((lim z->0 (sin(z)/z))x)".

[ascii]

well yes, but for this assignment my teacher said to allow the user to enter an expression such as:
(3x+2)(5x-1)

this is what you will have a good deal of the time when foiling, at least when factoring quadratic equations that are perfect square trinomials in either
ax^2+bx+c
x^2+bx+c

[helios]

My suggestion is that you simply divide the input string into digits and non-digits: "_3__2__5_-1_". As long as you don't need to validate user input, this is the simplest approach.

[ascii]

good idea! working on it now :)

[ascii]

thank you! it works now, here the functioning code :)

#include<iostream>
#include<cstring>
using std::cout;
using std::cin;
using std::endl;

const int max = 30;

void eatspaces(char* str)
{
	int i = 0;
	int j = 0;

	while((*(str + i) = *(str + j++)) != '\0')
		if (*(str + i) != ' ')
			i++;
	return;
}

class CFoil
{
private:
	int coefficient1;
	int coefficient2;
	int number1;
	int number2;
	bool co1;
	bool co2;
	bool num1; 
	bool num2;
	char* str;

	void calculate();
public:
	CFoil(char* pstr);
	~CFoil();
	void evaluate();
};

CFoil::~CFoil()
{
	str = NULL;
}

CFoil::CFoil(char* pstr):
	coefficient1(0), coefficient2(0), number1(0), number2(0), co1(true), co2(false), num1(false), num2(false)
{
	str = &(*pstr);
}

void CFoil::calculate()
{
	cout << coefficient1 * coefficient2 << "x^2+" 
		<< (coefficient1 * number2) + (coefficient2 * number1) 
		<< "x+" << number1 * number2 << endl;

	return;
}
void CFoil::evaluate()
{
	for(size_t i = 0; *(str+i) != '\0'; i++)
	{
		while(isdigit(*(str + i)))		// advance to the next number
			i++;

		if(num2)	 // grab the second number
		{
			if(*(str+i) == '-')
			{
				while(isdigit(*(str + ++i)))
				{
					number2 *= 10;
					number2 -= *(str+i) - '0';
				}
			}
			else
			{
				while(isdigit(*(str + ++i)))
				{
					number2 *= 10;
					number2 += *(str+i) - '0';
				}
			}
			num2 = false;
			calculate();
		}
		if(co2)		// grab the second coefficient
		{	
			if(*(str+i) == '-')
			{
				while(isdigit(*(str + ++i)))
				{
					coefficient2 *= 10;
					coefficient2 -= *(str+i) - '0';
				}
			}
			else
			{
				while(isdigit(*(str + ++i)))
				{
					coefficient2 *= 10;
					coefficient2 += *(str+i) - '0';
				}
			} 
			co2 = false;
			num2 = true;
		}
			
		if(num1)	// grab the first number
		{
			if(*(str+i) == '-')
			{
				while(isdigit(*(str + ++i)))
				{
					number1 *= 10;
					number1 -= *(str+i) - '0';
				}
			}
			else
			{
				while(isdigit(*(str + ++i)))
				{
					number1 *= 10;
					number1 += *(str+i) - '0';
				}
			}

			num1 = false;
			co2 = true;
		}
		if(co1)		// grab the first coefficient
		{
			if(*(str+i) == '-')
			{
				while(isdigit(*(str + ++i)))
				{
					coefficient1 *= 10;
					coefficient1 -= *(str+i) - '0';
				}
			}
			else
			{
				while(isdigit(*(str + ++i)))
				{
					coefficient1 *= 10;
					coefficient1 += *(str+i) - '0';
				}
			}

			co1 = false;
			num1 = true;
		}
	}

	return;
}

int main(void)
{
	char equation[max];  
	char* pequation = equation;
	cout << "Enter two binomials in parantheses, or an empty line to quit." << endl;
	for(;;)
	{
		CFoil foil(pequation);
		cin.getline(equation, max, '\n');
		eatspaces(pequation);
		if(!equation[0])
			exit(1);

		for(size_t i = 0; i < strlen(equation); i++)
		{
			if(!isdigit(*(pequation+i)) && *(pequation+i) != '-')		// turn all no numeric values into *
				*(pequation+i) = '*';
		}
		foil.evaluate();
	}

	return 0;
}