DocScript SVN

#include <iostream>


class Input;

double expression(Input&);
double term(Input&);
double factor(Input&);


using namespace std;


class Input {
		char const *ch;
	public:
		int operator()()        { return *ch; }
		Input& next()           { ++ch; return *this; }
		Input(char const *ch):  ch(ch) {}
};


double expression(Input& input)
{
	double value = term(input);
	while ( 1 )
		if ( input() == '+' )
			value += term(input.next());
		else if ( input() == '-' )
			value -= term(input.next());
		else
			break; 
	return value;
}

double term(Input& input)
{
	double value = factor(input);
	while ( 1 )
		if ( input() == '*' )
			value *= factor(input.next());
		else if ( input() == '/' )
			value /= factor(input.next());
		else
			break;
	return value;
}

double factor(Input& input)
{
	double value;
	if ( isdigit(input()) )
		value = input()-'0', input.next();
	else if ( input() == '(' ) {
		value = expression(input.next());
		if ( input() == ')' )
			input.next();
		else
			throw "')' expected"; }
	else
		throw "unexpectd character";
	return value;
}


int main(int argc, char *argv[])
{
	try {
		while ( *++argv ) {
			Input input(*argv);
			cout << *argv << '=' << expression(input) << endl;
		}
	}
	catch ( const char* exception ) {
		cerr << "Error: " << exception << endl;
		return 1;
	}
	return 0;
}