[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
  1 #include<iostream>
  2 #include<ctype.h>//isdigit()
  3 #include <cstring>
  4 #include<stack>
  5 using namespace std;
  6 
  7 stack<char> opCh;
  8 stack<long long> opNum;
  9 inline long long Calculate()
 10 {
 11     long long b = opNum.top();
 12     opNum.pop();
 13     long long a = opNum.top();
 14     opNum.pop();
 15     char operate = opCh.top();
 16     opCh.pop();
 17 
 18     switch (operate) 
 19     {
 20         case '+':
 21             return a + b;
 22         case '-':
 23             return a - b;
 24         case '*':
 25             return a * b;
 26         case '/':
 27             return a / b;
 28     }
 29 }
 30 inline long long Ojrank(char ch)
 31 {
 32     switch (ch) 
 33     {
 34         case '(':
 35             return 0;
 36         case '+':
 37         case '-':
 38             return 1;
 39         case '*':
 40         case '/':
 41             return 2;
 42         case ')':
 43             return 3;
 44     }
 45 }
 46 int main()
 47 {
 48     cout << "计算器1.0[仅支持整数的简单运算]" << endl;
 49     cout << "请输入计算表达式:" << endl;
 50     string expression;
 51     cin >> expression;
 52     int len = expression.length();
 53 
 54     long long topChRank, currentChRank;
 55     long long i = 0;
 56     long long number;
 57     while (expression[i] != '=' && expression[i] != '')
 58     {
 59         if (isdigit(expression[i]))//数字
 60         {
 61             number = 0;
 62             while (expression[i] != '=' && expression[i] != '' && isdigit(expression[i]))
 63             {
 64                 number = number * 10 + (expression[i]-'0');
 65                 i++;
 66             }
 67             opNum.push(number);
 68         }
 69         else//字符
 70         {
 71             if (opCh.empty()) {//字符栈为空
 72                 opCh.push(expression[i]);
 73                 i++;
 74                 continue;
 75             }
 76             topChRank = Ojrank(opCh.top());//获取优先级
 77             currentChRank = Ojrank(expression[i]);
 78             if (currentChRank == 0) {//左括号
 79                 opCh.push(expression[i]);
 80                 i++;
 81             }
 82             else if (currentChRank == 3) {//右括号
 83                 while (opCh.top() != '(') {
 84                     number = Calculate();
 85                     opNum.push(number);
 86                 }
 87                 opCh.pop();//弹出左括号
 88                 i++;
 89             }
 90             else {
 91                 while (!opCh.empty() && currentChRank <= topChRank)//优先级低的不能压在高的上面
 92                 {
 93                     number = Calculate();
 94                     opNum.push(number);;
 95                     topChRank = Ojrank(expression[i]);//即时更新栈顶字符优先级
 96                 }
 97                 opCh.push(expression[i]);
 98                 i++;
 99             }
100         }
101     }
102 
103     while (!opCh.empty())
104     {
105         number = Calculate();
106         opNum.push(number);
107     }
108     if(expression[len-1] == '=')
109         cout << expression << number << endl;
110     else
111         cout << expression <<'='<< number << endl;
112     return 0;
113 }
天涯犹在，不诉薄凉。