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SEEKING HELP FROM GURUS OF C++

vizorsx (2)
HELP ME GUYS PLEASE
Using the following grammar:

<expression> := <component> | <component> + <expression>
<component> := <factor> | <factor> + <component>
<factor> := <positive integer> | (<expression>)
write a program which analyses expressions conforming to the rules of this grammar and evaluates them, if the analysis has been successfully completed. It may be assumed that there is no overflow of float(C)/real(Pascal) numbers range.

Input

A integer n stating the number of expressions, then consecutive n lines, each containingan expression given as a character string.

Output

For each line value of the expression or output message ERROR if the expression does not follow the grammar.
Sample Input

5
32
12+34
1*(2+3)+3
1(2+3)+3
qwe323

Sample Output

32
46
8
ERROR
ERROR
Michaela Elise (117)
Here ya go. This is very similar to what you need. Have fun!!! :)


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/*
 * parser.cpp
 *
 *  Created on: Oct 2, 2012
 *      Author: michaela
 */

#include <iostream>
#include <fstream>
#include <string>

std::string s;
char token;
int error;

void exp(std::ofstream& outf, std::ifstream& inf);

void gettoken(std::ofstream& outf, std::ifstream& inf)
{
	static int pos = 0;
	token = s[pos];
	outf << "\n<gettoken> " << token << " ";
	if(token == '$')
		pos = 0;
	else
		++pos;
}

void digit(std::ofstream& outf, std::ifstream& inf)
{
	if(token != '$')
		outf << "<digit>";

	if(token >= '0' && token <= '9')
		gettoken(outf, inf);
	else
		error = 1;
}

void number(std::ofstream& outf, std::ifstream& inf)
{
	if(token != '$')
		outf << "<number>";

	digit(outf, inf);
}

void factor(std::ofstream& outf, std::ifstream& inf)
{
	if(token != '$')
		outf << "<factor>";

	if(token == '(')
	{
		gettoken(outf, inf);
		exp(outf, inf);
		if(token == ')')
			gettoken(outf, inf);
		else
			error = 2;
	}
	else
		number(outf, inf);
}

void term(std::ofstream& outf, std::ifstream& inf)
{
	outf << "<term>";

	factor(outf, inf);
	while(token == '*'){
		gettoken(outf, inf);
		factor(outf, inf);
	}
}

void exp(std::ofstream& outf, std::ifstream& inf)
{
	outf << "<exp>";

	term(outf, inf);
	while(token == '+')	{
		gettoken(outf, inf);
		term(outf, inf);
	}
}

int main()
{
	std::ifstream inf("in.dat");
	std::ofstream outf("out.dat");

	error = 0;

	while (!inf.eof())
	{
		getline(inf, s);
		std::cout << s << std::endl;

		gettoken(outf, inf);

		exp(outf, inf);
		if(error == 0)
			outf << "\nThe parse has been completed with no problems!!!\n\n";
		else
		{
			outf << "\nThe parse failed...\n";
			switch(error)
			{
			case 1:
				outf << "A digit did not follow an operator...\n";
				break;
			case 2:
				outf << "There was no closing parenthesis...\n";
				break;
			}
		}
	}

	inf.close();
	outf.close();

	return 0;
}



in.dat //so you can run it and see how it works

((2))$
3+4*5+6*7$
3*2+4*5+1$
3*(4+5)*(6+7)$
(2+(3+(4+5)))$
(2+3)*$
2+$
(2+3$


I used to have a more relevant example but I do not seem to have the code anymore :(
Last edited on
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