Calc.cpp

#include <iostream>
#include <stack>
#include <string>
#include <sstream>
#include <map>
#include <cassert>
#include <cstdlib>

using namespace std;

#define ERR err(__LINE__)

map<char, int> priority = {
	{ '\0', -256 },
	{ '(', -1 },
	{ ')', -1 },
	{ '+', 1 },
	{ '-', 1 },
	{ '*', 2 },
	{ '/', 2 },
};

stack<char>		op;
stack<double>	num;

void err(int line) {
	cout << "error at line " << line << endl;
	assert(0);
}

double popNum() {
	double a = num.top();
	num.pop();
	return a;
}

void popOp() {
	char c = op.top();
	if(c == '\0')
		ERR;

	if(c != '(') {
		cout << c << ' ';
		double b = popNum();
		double a = popNum();
		if(c == '+') { num.push(a+b); }
		if(c == '-') { num.push(a-b); }
		if(c == '*') { num.push(a*b); }
		if(c == '/') { num.push(a/b); }
	}
	op.pop();
}

int main() {
	cout << '>';

	op.push('\0');
	while(true) {
		string input;
		cin >> input;
		if(input == "end") {
			while(op.top() != '\0')
				popOp();
			break;
		}

		if(isdigit(input[0])) {
			num.push(atof(input.c_str()));
			cout << num.top() << ' ';
		}
		else {
			char c = input[0];

			if(c == '(') {
				op.push(c);
			}
			else if(c == ')') {
				if(op.top() == '(')
					ERR;

				while(op.top() != '(')
					popOp();
				popOp();
			}
			else {
				while(priority[c] <= priority[op.top()])
					popOp();
				op.push(c);
			}
		}
	}

	cout << endl << num.top() << endl;
}