#include <iostream>
#include <string>
#include <forward_list>
using namespace std;

struct token
{
    int prec_level;
    string tokenstr;
};

std::forward_list<token*> tokens;
std::forward_list<token*>::iterator it;
int tokenscount = 0;
void tokenize(string);
void createtoken(string,int);
int parse(int,int);
int parse_primary();
char peek_next_token();
int domath(char, int, int);
int conv_char_prec();

int main()
{
    cout << "Enter an equation with the operators /,*,+,-" << endl;
    string equation;
    int result;
    while (true)
    {
        getline(cin, equation);
        tokenize(equation);
        it = tokens.begin();
        result = parse(parse_primary(), 0);
        cout << result << endl;
        tokens.clear();
        tokenscount = 0;
    }
}

void tokenize(string equation)
{
    string cattoken;
    for (int i = 0; i < equation.length(); i++)
    {
        if (equation.at(i) == ' ')
            continue;
        else if (isdigit(equation.at(i)))
        {
            cattoken = equation.at(i);
            for (i+= 1; isdigit(equation.at(i)); i++)
            {
                ;
                cattoken.append(1, equation.at(i));
            }
            i--;
            createtoken(cattoken, NULL);
        }
        cattoken = equation.at(i);
        if (equation.at(i) == '+')
            createtoken(cattoken, 1);
        if (equation.at(i) == '-')
            createtoken(cattoken, 1);
        if (equation.at(i) == '*')
            createtoken(cattoken, 2);
        if (equation.at(i) == '/')
            createtoken(cattoken, 2);
    }
    createtoken(";", -1);

}

int parse(int lhs,int min_preclevel)
{
    int rhs;
    int lookahead = conv_char_prec();
    char oper = peek_next_token();
    while (lookahead >= min_preclevel)
    {
        int op = lookahead;
        rhs = parse_primary();
        lookahead = conv_char_prec();
        while (lookahead >= op)
        {
            rhs = parse(rhs, lookahead);
            lookahead = conv_char_prec();
        }
        lhs = domath(oper, lhs, rhs);

    }
    return lhs;

}

void createtoken(string tokenchar,int prec_level)
{
    token * tokenptr = new struct token;
    tokenptr->prec_level = prec_level;
    tokenptr->tokenstr = tokenchar;
    tokens.push_front(tokenptr);
}

int parse_primary()
{
    int lhs;
    advance(it, tokenscount);
    tokenscount = 1;
    lhs = stoi((*it)->tokenstr, nullptr, 10);
    return lhs;


}

char peek_next_token()
{
    advance(it, tokenscount);
    return (*it)->tokenstr.at(0);
}

int conv_char_prec()
{
    char lookahead = peek_next_token();
    int lookaheadprec;
    if (lookahead == '+')
        lookaheadprec = 1;
    if (lookahead == '-')
        lookaheadprec = 1;
    if (lookahead == '*')
        lookaheadprec = 2;
    if (lookahead == '/')
        lookaheadprec = 2;
    if (lookahead == ';')
        lookaheadprec = -1;
    return lookaheadprec;
}

int domath(char oper, int lhs, int rhs)
{
    int result;
    if (oper == '+')
        result = lhs + rhs;
    if (oper == '-')
        result = lhs - rhs;
    if (oper == '*')
        result = lhs * rhs;
    if (oper == '/')
        result = lhs / rhs;

    return result;
}