leetcode(c++)计算器类

#include <iostream>
#include <string>
#include <stack>

using namespace  std;

int calculator0(string s)
{
    stack<int>st;
    char opt = '+';
    int num = 0;
    for(int i = 0; i < s.size(); ++i)
    {
        char c = s[i];
        if(c>='0' && c <= '9')
        {
            num = num * 10 + (c - '0');
        }
        if(i == s.size() - 1 || c == '+' || c == '-')
        {
            if(opt == '+')
            {
                st.push(num);
            }
            else
            {
                st.push(-num);
            }
            opt = c;
            num = 0;
        }
    }
    int ans = 0;
    while(!st.empty())
    {
        ans += st.top();
        st.pop();
    }
    return ans;
}

int calculator1(string s)
{
    char opt = '+';
    stack<int>st;
    int num = 0;
    for(int i = 0; i < s.size(); ++i)
    {
        char c = s[i];
        if(c >= '0' && c <= '9')
        {
            num = num * 10 + (c - '0');
        }
        if(i == s.size() - 1 || c == '+' || c == '-' || c == '*' || c== '/')
        {
            if(opt == '+')
            {
                st.push(num);
            }
            else if(opt == '-')
            {
                st.push(-num);
            }
            else if(opt == '*')
            {
                int tmp = st.top() * num;
                st.pop();
                st.push(tmp);
            }
            else
            {
                float tmp = st.top() / num;
                st.pop();
                st.push(tmp);
            }
            opt = c;
            num = 0;
        }
    }
    int res = 0;
    while(!st.empty())
    {
        res += st.top();
        st.pop();
    }
    return res;
}
int i = 0;
int calculator2(string s)
{
    int num = 0;
    stack<int>st;
    char opt = '+';
    while(i < s.size())
    {
        char c = s[i++];
        if(c >= '0' && c <= '9')
        {
            num = num * 10 + (c - '0');
        }
        if(c == '(')num = calculator2(s);
        if(i >= s.size() || c == '+' || c == '-' || c == '*' || c == '/' ||  c == ')')
        {
            if(opt == '+')
            {
                st.push(num);
            }
            else if(opt == '-')
            {
                st.push(-num);
            }
            else if(opt == '*')
            {
                int tmp = st.top() * num;
                st.pop();
                st.push(tmp);
            }
            else if(opt == '/')
            {
                int tmp = st.top() / num;
                st.pop();
                st.push(tmp);
            }
            opt = c;
            num = 0;
        }
        if(c == ')')break;
    }
    int ans = 0 ;
    while(!st.empty())
    {
        // cout << st.top() << endl;
        ans += st.top();
        st.pop();
    }
    return ans;
}

int main()
{
    // //实现简单的只有+ - 的计算器
    // cout << calculator0("-2") << endl;
    // //实现包含+ - * /的计算器
    // cout << calculator1("9+2/3") << endl;

    //实现包含带()的计算器
    cout << calculator2("(1 + (4 + 5 +2) - 3)+(6+8)") << endl;
    cout << calculator2("(2 + 6 * 3 + 5- (3*14/7+2)*5)+3") << endl;
    cout << calculator2("1 + 1") << endl;
    return 0;
}