力扣224.基本计算器

• 一个栈存符号

  • 并记录当前数的符号
  • 遍历到一个数就存入答案

•   class Solution {public:int calculate(string s) {stack<int> st({1});int sign = 1;int res=0;int number;int n = s.size();int i=0;while(i<n) {if(isdigit(s[i])){number = 0;while(i < n && isdigit(s[i])){number = number * 10 + (s[i] - '0');i++;}res += sign * number;}else{if(s[i] == '+')sign = st.top();else if(s[i] == '-')sign = -st.top();else if(s[i] == '(')st.push(sign);else if(s[i] == ')')st.pop();i ++;}}return res;}};