How can I identify and solve the error in my exception handling?

[Shishykish]

Hello,

I am constructing a fractions calculator using classes. I have constructed the member functions with a try-catch-throw exception within a while loop to root out zero denominators. But when the compiler encounters one the member functions the console crashes :( when it meets a zero denominator instead of allowing me to enter new values for the fraction.

#include <iostream>

using namespace std;

class fractions{


private:
    int A,B,C,D, SUM;

public:
    fractions(int = 1, int = 1, int = 1, int = 1, int = 0);

    void show_fractions(float,float,float,float);
    float sum_of_fractions(float,float,float,float);
    float diff_of_fractions(float,float,float,float);
    float product_of_fractions(float,float,float,float);
    float division_of_fractions (float,float,float,float);
};

fractions::fractions(int a, int b, int c, int d, int sum)
{
    A = a;
    B = b;
    C = c;
    D = d;
    SUM = sum;

    cout << " The constructor has created 2 fractions in the form a/b and c/d with the following values for a,b,c and d respectively" << endl;
    cout << A << "  " << B << " " << C << " "<< D << endl;
}

void fractions::show_fractions(float A,float B,float C, float D)
{
    cout    << " The fractions are "
            << A << " / " << B << " and " << C << " / " << D << endl;
}

float fractions::sum_of_fractions(float A,float B,float C, float D)
{
    float denominator = 0;
    float sum = 0;

    cout << " The  2 fractions in the form a/b and c/d with the following values for a,b,c and d respectively" << endl;
    cout << A << "/" << B << " and " << C << "/"<< D << endl;

        denominator = (B * D);

    cout << " The denominator of " << B << " x " << D << endl;

    bool denominator_not_ok = true;

    while (denominator_not_ok)
    {
        try
        {
            if ((denominator == 0))
            {
                cout << "denominator is a zero value" << endl;
                throw denominator;
            }
        }
        catch (int e)
        {
            cout << " What are the values of A?" << endl;
            cin >> A;

            cout << " What are the values of B?" << endl;
            cin >> B;

            cout << " What are the values of B?" << endl;
            cin >> C;

            cout << "What is the value of D?"<< endl;
            cin >> D;
        }
        denominator_not_ok = false;
    }

    sum = (((A * D) + (C * B)) / (B * D));

cout << " The sum of 2 fractions in the form a/b and c/d with the following values for a,b,c and d respectively" << "   ";
cout << A << "/" << B << " and " << C << "/"<< D << endl;
cout << " is " << sum << endl;

return sum;

}

float fractions::diff_of_fractions(float A,float B,float C, float D)
{

    float denominator = 0;
    float sum = 0;

    cout << " The  2 fractions in the form a/b and c/d with the following values for a,b,c and d respectively" << endl;
    cout << A << "/" << B << " and " << C << "/"<< D << endl;

    denominator = (B * D);

    cout << " The denominator of (" << B << " x " << D << ")"<< endl;

    bool denominator_not_ok = true;

    while (denominator_not_ok)
    {
        try
        {
            if ((denominator == 0))
            {
                cout << "denominator is a zero value" << endl;
                throw denominator;
            }
        }
        catch (int e)
        {
            cout << " What are the values of A?" << endl;
            cin >> A;

            cout << " What are the values of B?" << endl;
            cin >> B;

            cout << " What are the values of B?" << endl;
            cin >> C;

            cout << "What is the value of D?"<< endl;
            cin >> D;
        }
        denominator_not_ok = false;
    }

    sum = (((A * D) - (C * B)) / (B * D));

cout << " The difference between 2 fractions in the form a/b and c/d with the following values for a,b,c and d respectively" << "   ";
cout << A << "/" << B << " - " << C << "/"<< D << " = " << sum << endl;

return sum;
}

float fractions::product_of_fractions(float A,float B,float C, float D)
{
    float denominator = 0;
    float sum = 0;

    denominator = (B * D);

    cout << " The denominator is (" << B << " x " << D << ")"<< endl;

    bool denominator_not_ok = true;

    while (denominator_not_ok)
    {
        try
        {
            if ((denominator == 0))
            {
                cout << "denominator is a zero value" << endl;
                throw denominator;
            }
        }
        catch (int e)
        {
            cout << " What are the values of A?" << endl;
            cin >> A;

            cout << " What are the values of B?" << endl;
            cin >> B;

            cout << " What are the values of B?" << endl;
            cin >> C;

            cout << "What is the value of D?"<< endl;
            cin >> D;
        }
        denominator_not_ok = false;
    }

    sum = ((A * C) / (B * D));

cout << " The difference between 2 fractions in the form a/b and c/d with the following values for a,b,c and d respectively" << "   ";
cout << A << "/" << B << " x " << C << "/"<< D << " = " << sum << endl;

return sum;
}

float fractions::division_of_fractions(float A,float B,float C, float D)
{
    float denominator = 0;
    float sum = 0;

    cout << " The  2 fractions in the form a/b and c/d with the following values for a,b,c and d respectively" << endl;
    cout << A << "/" << B << " and " << C << "/"<< D << endl;

    denominator = (B * C);

    cout << " The denominator of (" << B << " x " << C << ")"<< endl;

    bool denominator_not_ok = true;

    while (denominator_not_ok)
    {
        try
        {
            if ((denominator == 0))
            {
                cout << "denominator is a zero value" << endl;
                throw denominator;
            }
        }
        catch (int e)
        {
            cout << " What are the values of A?" << endl;
            cin >> A;

            cout << " What are the values of B?" << endl;
            cin >> B;

            cout << " What are the values of B?" << endl;
            cin >> C;

            cout << "What is the value of D?"<< endl;
            cin >> D;
        }
        denominator_not_ok = false;
    }

    sum = ((A * D) / (B * C));

cout << " The difference between 2 fractions in the form a/b and c/d with the following values for a,b,c and d respectively" << "   ";
cout << A << "/" << B << " / " << C << "/"<< D << " = " << sum << endl;

return sum;
}

int main()
{
    float A,B,C,D;

    cout << "To calculate the sum, difference, product and division of 2 fractions in the form A / B and C / D you need to enter some numbers" << endl;

    cout << "What are the values of A?" << endl;
    cin >> A;

    cout << "What are the values of B?" << endl;
    cin >> B;

    cout << "What are the values of B?" << endl;
    cin >> C;

    cout << "What is the value of D?"<< endl;
    cin >> D;

    cout << "The  2 fractions in the form a/b and c/d with the following values for a,b,c and d respectively" << endl;
    cout << A << "/" << B << " and " << C << "/"<< D << endl;

    fractions AA;

    //A.show_fractions(A,B,C,D);
    AA.sum_of_fractions(A,B,C,D);
    AA.diff_of_fractions(A,B,C,D);
    AA.product_of_fractions(A,B,C,D);
    AA.division_of_fractions(A,B,C,D);

    return 0;
}

[boost lexical cast]

1. Don't post the same question multiple times.

2. You don't need to use try catch blocks. Just use plain if statements.

[Shishykish]

Hello Boost,

Sorry, that's a school boy forum error move I know. I was just using a framework from a textbook I am using to teach myself C++. Is using if-else a better way that try-catch-throw?

I will give it a go. It's probably just a case of changing over a few commands in my current code.

[coder777]

Is using if-else a better way that try-catch-throw?

Yes.

In your case you catch an int value, but you do not throw an int hence you will not catch your own throw. You can simply put the catch block within the if block.

You always execute this line:

denominator_not_ok = false;

Hence the loop will always run only once. You may set it true in the else case.

[AbstractionAnon]

One obvious problem is the following:

Lines 60,112,158,207: You're throwing a float
Line 63,115,161,210: You're trying to catch an int.
Your catch block will never be invoked.

IMO, try/catch blocks are seldom useful within the same function. Exceptions should be used when a function has exhausted all error handling and wants to communicate the failure to higher level code. As boost lexical cast said, use if statements.

Lines 49-78, 101-130, 147-176, 196-225: Do you see a lot of repeated code here? That should be an indication to you that you need a function.

float fractions::check_denominator ()
{   cout << " The denominator is (" << B << " x " << D << ")"<< endl;    
    while (B * D == 0)  
    {  cout << "Denominator is 0" << endl;
        //   reenter A-D    
    }
    return B * D;
}

[Shishykish]

Hello AbstractionAnon,

Those tips have been very helpful and it all works a treat now! As for the code repetition, I have since moved on to a new chapter about static member functions. So I can now see how to implement your suggestion as such.