[栈/STL] 简易计算器

最近刚刚自学了一点点数据结构和STL,刚好写个简易的计算器    O(∩_∩)O

首先了解了一下逆波兰表达式

《大话数据结构》一书中阐释得较为易懂

 

 

 

 

 

#include<iostream>
#include<ctype.h>//isdigit()
#include <cstring>
#include<stack>
using namespace std;

stack<char> opCh;
stack<long long> opNum;
inline long long Calculate()
{
    long long b = opNum.top();
    opNum.pop();
    long long a = opNum.top();
    opNum.pop();
    char operate = opCh.top();
    opCh.pop();

    switch (operate) 
    {
        case '+':
            return a + b;
        case '-':
            return a - b;
        case '*':
            return a * b;
        case '/':
            return a / b;
    }
}
inline long long Ojrank(char ch)
{
    switch (ch) 
    {
        case '(':
            return 0;
        case '+':
        case '-':
            return 1;
        case '*':
        case '/':
            return 2;
        case ')':
            return 3;
    }
}
int main()
{
    cout << "计算器1.0[仅支持整数的简单运算]" << endl;
    cout << "请输入计算表达式:" << endl;
    string expression;
    cin >> expression;
    int len = expression.length();

    long long topChRank, currentChRank;
    long long i = 0;
    long long number;
    while (expression[i] != '=' && expression[i] != '')
    {
        if (isdigit(expression[i]))//数字
        {
            number = 0;
            while (expression[i] != '=' && expression[i] != '' && isdigit(expression[i]))
            {
                number = number * 10 + (expression[i]-'0');
                i++;
            }
            opNum.push(number);
        }
        else//字符
        {
            if (opCh.empty()) {//字符栈为空
                opCh.push(expression[i]);
                i++;
                continue;
            }
            topChRank = Ojrank(opCh.top());//获取优先级
            currentChRank = Ojrank(expression[i]);
            if (currentChRank == 0) {//左括号
                opCh.push(expression[i]);
                i++;
            }
            else if (currentChRank == 3) {//右括号
                while (opCh.top() != '(') {
                    number = Calculate();
                    opNum.push(number);
                }
                opCh.pop();//弹出左括号
                i++;
            }
            else {
                while (!opCh.empty() && currentChRank <= topChRank)//优先级低的不能压在高的上面
                {
                    number = Calculate();
                    opNum.push(number);;
                    topChRank = Ojrank(expression[i]);//即时更新栈顶字符优先级
                }
                opCh.push(expression[i]);
                i++;
            }
        }
    }

    while (!opCh.empty())
    {
        number = Calculate();
        opNum.push(number);
    }
    if(expression[len-1] == '=')
        cout << expression << number << endl;
    else
        cout << expression <<'='<< number << endl;
    return 0;
}