1using System;
2using System.Collections.Generic;
3
4public class BasicCalculatorII {
5    public int Calculate(string s) {
6        Stack<int> stack = new Stack<int>();
7        char sign = '+';
8        int num = 0;
9        for (int i = 0; i < s.Length; i++) {
10            char c = s[i];
11            if (Char.IsDigit(c)) {
12                num = num * 10 + (c - '0');
13            }
14            if (!Char.IsDigit(c) && c != ' ' || i == s.Length - 1) {
15                if (sign == '+') {
16                    stack.Push(num);
17                } else if (sign == '-') {
18                    stack.Push(-num);
19                } else if (sign == '*') {
20                    stack.Push(stack.Pop() * num);
21                } else if (sign == '/') {
22                    stack.Push(stack.Pop() / num);
23                }
24                sign = c;
25                num = 0;
26            }
27        }
28
29        int result = 0;
30        while (stack.Count != 0) {
31            result += stack.Pop();
32        }
33        return result;
34    }
35
36    public static void Main() {
37        BasicCalculatorII calculator = new BasicCalculatorII();
38        Console.WriteLine("Output: " + calculator.Calculate("3+2*2"));
39    }
40}

1