C++实现简易计算器

来源：互联网发布：上海数据交易中心 coo 编辑：程序博客网时间：2024/06/06 01:40
1.原理：利用栈的原理，将表达式转化为后缀表达式然后计算
2.代码：
#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<<"后缀表达式为："<<postfixExp<<endl;    cout<<"表达式的值为：";    printf("%.2f\n",ans);}double Calculator::calculate(string infixExp){        this->infixExp= infixExp;        if (infix_to_postfix()){            return ans=cal_postfix();        }else{           cout<<"语法错误，请检查表达式"<<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<<"输入要计算的表达式(以字母Q结束程序)："<<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;}
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