c++实现简单计算器

帮一个同学写的，非计算机类专业，应付交差，也没什么功能，两个数的加减乘除运算，以及三角函数的运算。要求用到模板、运算符重载和异常处理。

一直以来都是用的java，没怎么用过c++，就当是复习了一下c++语法。

代码如下：

 #include<iostream>
 #include<string>
 #include<cmath>
 #include<cstdlib>

 using namespace std;

 //四则运算
 template <class T> class ElementaryArithmetic{
 private:
     T result;
     T operand1, operand2;
     char operators;
 public:
     //四则运算
     void Calculate();
     //加法运算
     void add(T, T);
     //减法运算
     void subtraction(T, T);
     //乘法运算
     void multiplication(T, T);
     //除法运算
     void divide(T, T);
     //输出运算符重载
     template <class E> friend ostream &operator<<(ostream&, ElementaryArithmetic<E> &);
 };

 //四则运算
 template <class T> void ElementaryArithmetic<T>::Calculate(){
     int type;

 loop1:
     system("cls");
     cout << endl << "*******************" << endl;
     cout << "*   1.加法运算    *" << endl;
     cout << "*   2.减法运算    *" << endl;
     cout << "*   3.乘法运算    *" << endl;
     cout << "*   4.除法运算    *" << endl;
     cout << "*******************" << endl << endl;
     cout << "请输入菜单项(1-4)：";
     try{
         cin >> type;
         if (type !=  && type !=  && type !=  && type != )
             throw ;
     }
     catch (int e){
         cout << endl << "输入错误，请重新输入选项...";
         system("pause");
         goto loop1;
     }

     cout << endl << "请输入两个数字：";
     cin >> operand1 >> operand2;
     if (type == ){
         add(operand1, operand2);
         operators = '+';
     }
     else if (type == ){
         subtraction(operand1, operand2);
         operators = '-';
     }
     else if (type == ){
         multiplication(operand1, operand2);
         operators = '*';
     }
     else if (type == ){
         divide(operand1, operand2);
         operators = '/';
     }

 }

 //加法运算
 template <class T> void ElementaryArithmetic<T>::add(T operand1,T operand2){
     result = operand1 + operand2;
 }

 //减法运算
 template <class T> void ElementaryArithmetic<T>::subtraction(T operand1, T operand2){
     result = operand1 - operand2;
 }

 //乘法运算
 template <class T> void ElementaryArithmetic<T>::multiplication(T operand1, T operand2){
     result = operand1 * operand2;
 }

 //除法运算
 template <class T> void ElementaryArithmetic<T>::divide(T operand1, T operand2){
     try{
         //除数为0，出现异常
         if ((operand2 - ) < 1e- && (operand2 - ) > -1e-)
             throw ;
     }
     catch (int){
         throw ;
     }
     result = operand1 / operand2;
 }

 //输出运算符重载
 template <class E> ostream& operator<<(ostream &os, ElementaryArithmetic<E> &result){
     os << endl << "计算结果 ： " << result.operand1 << result.operators << result.operand2 << '=' << result.result << endl;
     return os;
 }

 //三角函数
 class Trigonometric{
 private:
     double radian;
     string type;
     double result;
 public:
     //三角函数计算
     void Calculate();
     //输出运算符重载
     friend ostream &operator<<(ostream&, Trigonometric &);
 };

 //三角函数计算
 void Trigonometric::Calculate(){
     int option;

 loop2:
     system("cls");
     cout << "*******************" << endl;
     cout << "*    1.求正弦      *"<< endl;
     cout << "*    2.求余弦      *"<< endl;
     cout << "*    3.求正切      *"<< endl;
     cout << "*******************" << endl << endl;
     cout << "请输入菜单项(1-3)：";
     try{
         cin >> option;
         if (option !=  && option !=  && option !=  && option != )
             throw ;
     }
     catch (int e){
         cout << endl << "输入错误，请重新输入选项..." ;
         system("pause");
         goto loop2;
     }

     cout << endl << "请输入弧度：";
     cin >> radian;

     if (option == ){
         result = sin(radian);
         type = "sin";
     }
     else if (option == ){
         result = cos(radian);
         type = "cos";
     }
     else if (option == ){
         result = tan(radian);
         type = "tan";
     }
 }

 //输出运算符重载
 ostream &operator<<(ostream &os, Trigonometric &result){
     os << endl << "计算结果 ： " << result.type << "(" << result.radian << ") = " << result.result << endl;
     return os;
 }

 int main(){
     int type;

 loop:
     while (true){
         system("cls");
         cout << "*******主菜单**********" << endl;
         cout << "*                     *" << endl;
         cout << "*   1. 四则运算       *" << endl;
         cout << "*   2. 三角函数       *" << endl;
         cout << "*   3. 退出程序       *" << endl;
         cout << "*                     *" << endl;
         cout << "***********************" << endl << endl;
         cout << "请输入菜单项(1-3)：";

         try{
             cin >> type;
             if (type !=  && type !=  && type != )
                 throw - ;

             if (type == ){
                 ElementaryArithmetic<double> calc;
                 calc.Calculate();
                 cout << calc;
             }
             else if (type == ){
                 Trigonometric calc;
                 calc.Calculate();
                 cout << calc;
             }
             else if (type == )
                 break;
         }
         catch (int e){
             if (e == -){
                 cout << endl << "输入错误，请重新输入选项...";
                 system("pause");
                 goto loop;
             }
             else if (e == )
                 cout << "除数不能为 0 " << endl;

         }
         cout << endl;
         system("pause");
     }
     return ;
 }

好吧，其实我也不知道为什么要求用模板和运算符重载，感觉没什么必要，典型的作业代码，不过也可能是我思想的局限性。总之，就这样吧。