Basic Calculator II.cpp

#include <string>

using namespace std;

class Solution {
public:
    int calculate(string s)
    {
        long res = 0, curRes = 0, num = 0, n = s.size();
        char op = '+';
        for(int i = 0; i < n; i++)
        {
            char c = s[i];
            if(c >= '0' && c <= '9')
            {
                num = num * 10 + c - '0';
            }
            if(c == '+' || c == '-' || c == '*' || c == '/' || i == n - 1)
            {
                switch(op){
                    case '+':{
                        curRes += num;
                        break;
                    }
                    case '-':{
                        curRes -= num;
                        break;
                    }
                    case '*':{
                        curRes *= num;
                        break;
                    }
                    case '/':{
                        curRes /= num;
                        break;
                    }
                }
                if(c == '+' || c == '-' || i == n - 1)
                {
                    res += curRes;
                    curRes = 0;
                }
                op = c;
                num = 0;
            }
        }
        return res;
    }
};