C++實現簡易計算器

1.原理：利用棧的原理，將表達式轉化爲後綴表達式然後計算

2.代碼：

#include<iostream>
#include<cmath>
#include<sstream>
#include<cstdio>
using namespace std;
template <class T>
class Stack{
private :
     T data[1000];
     int t;
public :
     Stack(){t=0;}
     void clear(){t=0;}
     T pop(){
       if (t<=0) {
            cout<<"stack is empty"<<endl;
            return data[0];
        }
        t--;
        //cout<<"pop "<<data[t]<<endl;
        return data[t];
     }
     void push(T x){
       if(t>=1000){
        cout<<"the stack is full"<<endl;
        return;
       }
       //cout<<"push "<<x<<endl;
       data[t++]=x;
     }
     T top(){
       if(t<=0){
        cout<<"the stack is empty"<<endl;
        return data[0];
       }
       return data[t-1];
     }
     bool is_empty(){
        if(t<=0) return true;
        return false;
     }
};

class Calculator{
private :
     string postfixExp;
     string infixExp;
     double ans;
public :
     Calculator(string s=""){
       infixExp=s;
       ans=0;
     }
     void display();
     double calculate(string infixExp);
     bool infix_to_postfix();
     double  cal_postfix();
     double cal(double ,double ,char);
     string change(double);
     int get_priority(char);
     double read_num(string s,int *pos);
};
void Calculator::display()
{
    cout<<"後綴表達式爲："<<postfixExp<<endl;
    cout<<"表達式的值爲：";
    printf("%.2f\n",ans);
}
double Calculator::calculate(string infixExp){
        this->infixExp= infixExp;
        if (infix_to_postfix()){
            return ans=cal_postfix();
        }else{
           cout<<"語法錯誤，請檢查表達式"<<endl;
           return 0.0;
        }
}
double Calculator::read_num(string s,int *pos)
{
    double x=0;
    int flag=0,w=0,h=1,i;
    if(s[(*pos)]=='-') {(*pos)++;h=-1;}
    for ( i=(*pos);i<s.length();i++)
    if (s[i]!='#')
        if(s[i]=='.'){
            flag=1;
        }else {
            if(flag) w++;
            x=x*10+s[i]-'0';
    }else  break;
    (*pos)=i;
    return x/pow(10,w)*h;
}
string Calculator::change(double x){
     int y = (int)(x*10000),yy = y%10000;
     stringstream ss;
     ss<<y/10000<<'.'<<yy/1000<<(yy%1000)/100<<(yy%100)/10<<(yy%10);
     string r;
     ss>>r;
     int i;
     for (i=r.length()-1;i>=0;i--)
        if(r[i]!='0') break;
     if (r[i]=='.') i--;
     return  r.assign(r,0,i+1);
}
double Calculator::cal(double num1,double num2,char op)
{
    switch(op){
  case '+':
      return num1+num2;
  case '-':
      return num1-num2;
  case '*':
      return num1*num2;
  case '/':
      return num1/num2;
  default:
     return 0.0;
    }
}

int Calculator::get_priority(char c){
    switch(c){
      case '+':case '-': return 1;
      case '*':case '/': return 2;
      case '(':return 0;
      case ')':return 0;
      case '#':return -2;
      default:
        return -1;
    }
}
bool Calculator::infix_to_postfix()
{
    Stack<char> stk;
    int a_num_end=0,is_negative=0;
    string result="#";
    stk.push('#');
    for (int i=0;i<infixExp.length();i++)
    {
        char c = infixExp[i];
        if(c=='-'&&(i==0||infixExp[i-1]=='(')) {result+='-'; is_negative=1;continue;}
        if((c<='9'&&c>='0')||c=='.') {
                if(a_num_end&&!is_negative) {result+='#'; }
                is_negative=0;
                result+=c;
                a_num_end=0;
        }
        else{a_num_end=1;
         if(c=='(') stk.push('(');
        else if (c==')') {
                while (stk.top()!='(')
                {
                    result+='#';
                    result+=stk.pop();
                }
                stk.pop();
            }
        else {
             int p = get_priority(c);
             if (p==-1) return false;
             while (p<=get_priority(stk.top())){
                result+='#';
                result+=stk.pop();
             }
             stk.push(c);
        }
        }
    }
    while (stk.top()!='#'){
        result+='#';
        result+=stk.pop();
    }
    result+='#';
    cout<<result<<endl;
    postfixExp = result;
    return true;
}
double Calculator::cal_postfix()
{
    int l = postfixExp.length();
    Stack<double> stk1;
    for (int i=1;i<l;i++){
        char c = postfixExp[i];
        if (c=='#') continue;
        if((c=='-'&&postfixExp[i+1]!='#')||(c>='0'&&c<='9')) stk1.push(read_num(postfixExp,&i));
        else {
           double y  = stk1.pop();
           double x = stk1.pop();
           stk1.push(cal(x,y,c));
        }
    }
   return stk1.pop();
}
int main()
{
    Calculator c;
    string ini;
  while (1){
        cout<<"輸入要計算的表達式(以字母Q結束程序)："<<endl;
        cin>>ini;
        if(ini.length()==1&&ini[0]=='Q') break;
        c.calculate(ini);
        c.display();
    }
    //c.calculate("(-5)*10+20/20-2*3*6/36");
    //c.display();
    return 0;
}