Исключения

//error4.cpp – using exception classes
#include <iostream>
#include <cmath> // or math.h, unix users may need -lm flag
#include "exc_mean.h"
// function prototypes
double hmean(double a, double b);
double gmean(double a, double b);
int main()
{
    using std::cout;
    using std::cin;
    using std::endl;
    
    double x, y, z;
 
    cout << "Enter two numbers: ";
    while (cin >> x >> y)
    {
        try {                  // start of try block
            z = hmean(x,y);
            cout << "Harmonic mean of " << x << " and " << y
                << " is " << z << endl;
            cout << "Geometric mean of " << x << " and " << y
                << " is " << gmean(x,y) << endl;
            cout << "Enter next set of numbers <q to quit>: ";
        }// end of try block
        catch (bad_hmean & bg)    // start of catch block
        {
            bg.mesg();
            cout << "Try again.\n";
            continue;
        }                  
        catch (bad_gmean & hg) 
        {
            cout << hg.mesg();
            cout << "Values used: " << hg.v1 << ", " 
                 << hg.v2 << endl;
            cout << "Sorry, you don't get to play any more.\n";
            break;
        } // end of catch block
    }
    cout << "Bye!\n";
    // cin.get();
    // cin.get();
    return 0;
}
 
double hmean(double a, double b)
{
    if (a == -b)
        throw bad_hmean(a,b);
    return 2.0 * a * b / (a + b);
}
 
double gmean(double a, double b)
{
    if (a < 0 || b < 0)
        throw bad_gmean(a,b);
    return std::sqrt(a * b); 
}

// exc_mean.h  -- exception classes for hmean(), gmean()
#include <iostream>
 
class bad_hmean
{
private:
    double v1;
    double v2;
public:
    bad_hmean(double a = 0, double b = 0) : v1(a), v2(b){}
    void mesg();
};
 
inline void bad_hmean::mesg()
{   
    std::cout << "hmean(" << v1 << ", " << v2 <<"): "
              << "invalid arguments: a = -b\n";
}
 
class bad_gmean
{
public:
    double v1;
    double v2;
    bad_gmean(double a = 0, double b = 0) : v1(a), v2(b){}
    const char * mesg();
};
 
inline const char * bad_gmean::mesg()
{  
    return "gmean() arguments should be >= 0\n";
}

#include <iostream>
#include <stdexcept>
#include <string>
 
class my_except
    : public std::logic_error
    {   // base of all invalid-argument exceptions
public:
    typedef std::logic_error _Mybase;
 
    explicit my_except(const std::string& _Message)
        : _Mybase(_Message.c_str())
        {   // construct from message string
        }
 
    explicit my_except(const char *_Message)
        : _Mybase(_Message)
        {   // construct from message string
        }
 
 #if _HAS_EXCEPTIONS
 
 #else /* _HAS_EXCEPTIONS */
protected:
    virtual void _Doraise() const
        {   // perform class-specific exception handling
        _RAISE(*this);
        }
 #endif /* _HAS_EXCEPTIONS */
    };
 
 
 
int main()
{
    int n = 0;
 
    try
    {
        if (n == 0)
            throw my_except("ZERO");
    }
    catch (std::logic_error& le)
    {
        std::cout << le.what() << std::endl;
    }
 
    return 0;
}