简易四则运算计算器

  1 #include <string>
  2 #include <stack>
  3 #include <vector>
  4 
  5 class Element {
  6 public:
  7     static Element MakeData(double value_) {return Element(DATA, value_, ‘ ‘);}
  8     static Element MakeOp(char op) {return Element(OP, 0.0, op);}
  9     bool isData() const { return t == DATA; }
 10     bool isOp() const { return t == OP; }
 11     char getOp() const { return op;}
 12     double getValue() const { return value; }
 13     int priority() const {
 14         if (isOp()) {
 15             if (getOp() == ‘*‘ || getOp() == ‘/‘) {
 16                 return 2;
 17             } else if (getOp() == ‘+‘ || getOp() == ‘-‘) {
 18                 return 1;
 19             } else if (getOp() == ‘(‘ || getOp() == ‘)‘) {
 20                 return 0;
 21             }
 22         }
 23         return -1;
 24     }
 25 private:
 26     enum Type {DATA, OP};
 27     Type t;
 28     double value;
 29     char op;
 30     Element(Type t_, double value_, char op_) : t(t_), value(value_), op(op_) {}
 31  };
 32 
 33 bool isOp(char c) {
 34     return c == ‘+‘ || c == ‘-‘ || c == ‘*‘ || c == ‘/‘ || c == ‘(‘ || c == ‘)‘;
 35 }
 36 
 37 using std::string;
 38 using std::vector;
 39 using std::stack;
 40 
 41 vector<Element> str2mid(const string &input) {
 42     vector<Element> mid;
 43     string data;
 44     for (size_t i = 0; i < input.length(); i++) {
 45         if (isOp(input[i])) {
 46             if (data != "") {
 47                 mid.push_back(Element::MakeData(std::stod(data)));
 48                 data = "";
 49             }
 50             mid.push_back(Element::MakeOp(input[i]));
 51         } else if (!isspace(input[i])){
 52             data += input[i];
 53         }
 54     }
 55     if (data != "") {
 56         mid.push_back(Element::MakeData(std::stod(data)));
 57         data = "";
 58     }
 59     return mid;
 60 }
 61 
 62 vector<Element> mid2post(const vector<Element> &mid) {
 63     stack<Element> s;
 64     vector<Element> post;
 65     for (auto it = mid.begin(); it != mid.end(); it++) {
 66         if (it->isData()) { // 如果是操作数，直接输出
 67             post.push_back(*it);
 68         } else if (it->isOp() && it->getOp() == ‘(‘) { // 如果是‘(‘直接入栈
 69             s.push(*it);
 70         } else if (it->isOp() && it->getOp() == ‘)‘) { // 如果是‘)‘将栈中‘(‘之后的操作符出栈
 71             while(!s.empty() && s.top().getOp() != ‘(‘) {
 72                 post.push_back(s.top());
 73                 s.pop();
 74             }
 75             s.pop();
 76         } else if (it->isOp()) { // 如果是操作符 出栈直到栈顶优先级低于该操作符，其中‘(‘的优先级最低，然后把该操作符入栈
 77             while(!s.empty() && s.top().priority() >= it->priority()) {
 78                 post.push_back(s.top());
 79                 s.pop();
 80             }
 81             s.push(*it);
 82         }
 83     }
 84     while(!s.empty()) { // 栈中元素全部出栈
 85         post.push_back(s.top());
 86         s.pop();
 87     }
 88     return post;
 89 }
 90 
 91 double calc_post(const vector<Element> &post) {
 92     stack<Element> s;
 93     for (auto it = post.begin(); it != post.end(); it++) {
 94         if (it->isData()) {
 95             s.push(*it);
 96         } else if (it->isOp()) {
 97             double op_2 = s.top().getValue();
 98             s.pop();
 99             double op_1 = 0;
100             if (!s.empty()) { //处理开头为-的情况
101                 op_1 = s.top().getValue();
102                 s.pop();    
103             }
104             char op = it->getOp();
105             if (op == ‘+‘) {
106                 s.push(Element::MakeData(op_1 + op_2));
107             } else if (op == ‘-‘) {
108                 s.push(Element::MakeData(op_1 - op_2));
109             } else if (op == ‘*‘) {
110                 s.push(Element::MakeData(op_1 * op_2));
111             } else if (op == ‘/‘) {
112                 s.push(Element::MakeData(op_1 / op_2));
113             }
114         }
115     }
116     return s.top().getValue();
117 }
118 
119 double calc(const std::string &input) {
120     return calc_post(mid2post(str2mid(input)));
121 }