C++实现简易计算器

#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()
{

4000
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;
}