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 != 1 && type != 2 && type != 3 && type != 4)
            throw 1;
    }
    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 == 1){
        add(operand1, operand2);
        operators = '+';
    }
    else if (type == 2){
        subtraction(operand1, operand2);
        operators = '-';
    }
    else if (type == 3){
        multiplication(operand1, operand2);
        operators = '*';
    }
    else if (type == 4){
        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 - 0) < 1e-8 && (operand2 - 0) > -1e-8)
            throw 0;
    }
    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 != 1 && option != 2 && option != 3 && option != 4)
            throw 2;
    }
    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 == 1){
        result = sin(radian);
        type = "sin";
    }
    else if (option == 2){
        result = cos(radian);
        type = "cos";
    }
    else if (option == 3){
        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 != 1 && type != 2 && type != 3)
                throw - 1;
        
            if (type == 1){
                ElementaryArithmetic<double> calc;
                calc.Calculate();
                cout << calc;
            }
            else if (type == 2){
                Trigonometric calc;
                calc.Calculate();
                cout << calc;
            }
            else if (type == 3)
                break;
        }
        catch (int e){
            if (e == -1){
                cout << endl << "输入错误，请重新输入选项...";
                system("pause");
                goto loop;
            }
            else if (e == 0)
                cout << "除数不能为 0 " << endl;
            
        }
        cout << endl;
        system("pause");
    }
    return 0;
}

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。