栈计算器 Calculator1.0

来源：互联网发布：击剑器材数据编辑：程序博客网时间：2024/05/22 09:44

花了大概三天的零碎时间学习了用栈实现计算器（可用于小数点以及多位数的计算）。下面转来了一篇前人的代码，而且把自己的理解作为注释写入。

. 就目前所学，还写不出其他什么值得记录的东西。先这样O(∩_∩)O

#include <iostream>  #include <string>  #include <stack>  #include<cctype> using namespace std;bool IsOne(char c){return (c == '+' || c == '-');}bool IsTwo(char c){return (c == '*' || c == '/');}string Infix_Postfix(string Infix){//中缀改后缀stack<char> stack;string result;for (int i = 0; i<Infix.size(); i++){if (isdigit(Infix[i]) || Infix[i] == '.')//函数isdigit()， 参数是数字，返回真{    while (isdigit(Infix[i]) || Infix[i] == '.') {result += Infix[i++]; }i--;//while循环最后多加了一次，减回去.*result += ' '; //不同数字之间用空格隔开 }else if (IsOne(Infix[i])){ //读到一级运算符while (stack.size() && (IsOne(stack.top()) || IsTwo(stack.top()))){ //A&&(B||C)形式result += stack.top();stack.pop();}stack.push(Infix[i]);}else if (Infix[i] == ')'){  //括号优先while (stack.top() != '('){result += stack.top();stack.pop();}stack.pop();//最后记得弹出"("}else if (IsTwo(Infix[i])){  //读到二级运算符while (stack.size() && IsTwo(stack.top())){result += stack.top();stack.pop();}stack.push(Infix[i]);//压入二级运算符}else stack.push(Infix[i]);}while (stack.size()){ result += stack.top();stack.pop();}return result;}double TenTimes(int n){double res = 1;for (int i = 0; i<n; i++){res *= 10;}return res;}double Achieve(string s){ // 实现了大于9以及小数的计算double res = 0;char c;int dec = 0;for (int i = 0; i < s.size(); i++){c = s[i ];if (c == '.')  dec = i; //标记小数点在第几位else if (!dec) res = res * 10 + c - '0';//只要往后一位，前面的计算结果*10else res += (c - '0') / TenTimes(i-dec);//计算小数值}return res;}double Calculate(string s){double res, t;stack<double> num;string temp;for (int i = 0; i<s.size(); i++){temp = "";if (isdigit(s[i]) || s[i] == '.'){while (isdigit(s[i]) || s[i] == '.') temp += s[i++]; //如果最后一位是数字，这样做会出错   num.push(Achieve(temp));}else{switch (s[i]){case '+': t = num.top(); num.pop(); t += num.top(); num.pop(); num.push(t); break;case '-': t = num.top(); num.pop(); t = num.top() - t; num.pop(); num.push(t); break;case '*': t = num.top(); num.pop(); t *= num.top(); num.pop(); num.push(t); break;case '/': t = num.top(); num.pop(); t = num.top() / t; num.pop(); num.push(t); break;default: cerr << "Fatal Error! Result would be wrong!" << endl; system("pause"); break;}}}res = num.top();return res;}int main(){string mid, result;cin >> mid;result = Infix_Postfix(mid);cout << "Infix change to Postfix： " << endl;cout << result << endl;cout << "The result is: " << Calculate(result) << endl;system("pause");return 0;}

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