Thread: Fraction Class

Assignment:

Design a fraction class.

A fraction is a number made up of a numerator and a denominator. Design a class to implement this.

Obviously we’d like to be able to use the normal operators for mathematical operations (+,-,*, /), comparison operations(==, !=, and <), incrementation, decrementation, input and output.

We don’t need to worry about reducing the fraction. In other words, 4/2 is fine, there’s no need to runt hat into 2/1.

Incrementation and decrementation should add or subtract (as appropriate) 1/1 to the object. Input is in the form of “num denom”. Output is in the form “num/denom”

Code:

#include <iostream>
#include <string>
using namespace std;


class fraction {
private:
    int numerator;
    int denominator;


public:
    int getNum() {return numerator;}
    int getDenom() {return denominator;}
    fraction();
    fraction(int,int);
    //fraction(int num = 1, int denom = 1):numerator(num), denominator(denom) {}
    fraction operator+(fraction);
    fraction operator-(fraction);
    fraction operator*(fraction);
    fraction operator/(fraction);
    fraction& operator++();
    fraction& operator--();
    bool operator==(fraction);
    bool operator!=(fraction);
    bool operator<(fraction);
    friend ostream& operator<<(ostream &out, const fraction& value);
    friend istream& operator>>(istream &in, fraction& value);
    string print();
};


fraction::fraction(int num, int denom){
    numerator = num;
    denominator = denom;
}


fraction fraction::operator+(fraction Frac){
    if(numerator == 0 || Frac.getNum() == 0){
        if (numerator != 0){
            return fraction(numerator,denominator);
        }
        else{
        return fraction(Frac.getNum(),Frac.getDenom());
        }
    }
    else{ 
        return fraction((numerator*Frac.getDenom()) + (denominator*Frac.getNum()), denominator*Frac.getDenom());
        }
    
}


fraction fraction::operator-(fraction Frac){
    if(numerator == 0 || Frac.getNum() == 0){
        if (numerator != 0){
            return fraction(numerator,denominator);
        }
        else{
        return fraction(Frac.getNum(),Frac.getDenom());
        }
    }
    else{ 
        return fraction((numerator*Frac.getDenom()) - (denominator*Frac.getNum()), denominator*Frac.getDenom());
        }
    
}


fraction fraction::operator*(fraction Frac){
    return fraction((Frac.getNum()*numerator), (Frac.getDenom()*denominator));
}


fraction fraction::operator/(fraction Frac){
    return fraction((Frac.getNum()*denominator), (Frac.getDenom()*numerator));
}


bool fraction::operator==(fraction Frac){
return((Frac.getNum() == numerator) && (Frac.getDenom() == denominator));
}


bool fraction::operator!=(fraction Frac){
return((Frac.getNum() != numerator) || (Frac.getDenom() != denominator));
}


bool fraction::operator<(fraction Frac){
double first, second;
    if(denominator != 0){
        first = numerator/ (double) denominator;
    }
    else{
        first = 0.0;
    }
    if(Frac.getDenom() != 0){
        second = Frac.getNum()/ (double) Frac.getDenom();
    }
    else{
        second = 0.0;
    }
    return(first < second);
}


fraction& fraction::operator++(){
    if(denominator != 0){
        numerator += denominator;
        return *this;
    }
    else{
        cout<< "Enter a proper fraction!";
    }


}


fraction& fraction::operator--(){
    if(denominator != 0){
        numerator -= denominator;
        return *this;
    }
    else{
        cout<< "Enter a proper fraction!";
    }


}


ostream &operator<<(ostream& out, const fraction& value){
    out<< value.numerator<<"/"<<value.denominator;
    return out;
}


istream& operator>>(istream &in, fraction& value){
    int num, denom;
    in>>num>>denom;
    value = fraction(num, denom);
    return in;
}


int main(){
    int Num2, Denom2;
    fraction f1,f2;


    cout<< "Enter the first numerator: ";
    cin>> Num2;
    cout<< "Enter the first denominator: ";
    cin>> Denom2;
    f1(Num2,Denom2);
    cout<<"The first fraction is: "<<f1.print()<<endl;


    cout<< "Enter the second numerator: ";
    cin>> Num2;
    cout<< "Enter the second denominator: ";
    cin>> Denom2;
    f2(Num2,Denom2);
    cout<<"The second fraction is: "<<f1.print()<<endl;


    cout<<"The following operations were performed:"<<endl;


    fraction f3 = f1 + f2;
    cout<<"Addition: "<<f1.print() << " + " << f2.print() << " = " << f3.print()<<endl;


    f3 = f1 - f2;
    cout<<"Subtraction: "<<f1.print() << " - " << f2.print() << " = " << f3.print()<<endl;


    f3 = f1 * f2;
    cout<<"Multiplication: "<<f1.print() << " * " << f2.print() << " = " << f3.print()<<endl;


    f3 = f1 / f2;
    cout<<"Division: "<<f1.print() << " ÷ " << f2.print() << " = " << f3.print()<<endl;


    ++f1;
    cout<<"Incrementation: "<<f1.print() << " ++ " << " = " << f1.print()<<endl;


    --f2;
    cout<<"Decrementation: "<<f2.print() << " -- " << " = " << f2.print()<<endl;


}

I keep getting an error: error C2064: term does not evaluate to a function taking 2 arguments.
This is in reference to line 158 and 166
Any ideas on what I'm doing wrong? Does the code make sense in general?

Looking at:

Code:

f1(Num2,Denom2);

My guess is that you want to create f1 by calling its constructor with the two arguments. If so, you should write:

Code:

fraction f1(Num2,Denom2);

In fact, variables should be declared near first use, so doing this is good practice. The same goes for f2.

The warnings about "not all control paths return a value" just means that there is a condition in which the function has no return statement that will be executed, yet it is declared as returning a value. In this case, an appropriate solution is to throw an exception instead of just printing an error message.

As for the error: you did not implement the print member function yet you called it several times. In fact, since you overloaded operator<< you don't need the print member function to begin with.

You may have fixed the compiler errors, but you have several other issues, including but not limited to:

Not implementing both pre and post increment / decrement.
Lack of const-correctness.
having cout statements inside the increment/decrement. (Consider exceptions instead)
With the absense of reducing the fraction, you should be doing some extra work to ensure that the fractions 4/2 and 2/1 compare equal, for example.
The far better way to implement operator less-than is to rearrange the use of division into a multiplication.
Operator >> does not mirror operator << (it does not skip the slash).

(a/b < c/d)
will be the same as

(a*d < c*b)

but the second expression is quicker

Originally Posted by vart

(a/b < c/d)
will be the same as

(a*d < c*b)

but the second expression is quicker

Yes, and it avoids the need to test for zero demoninators first since it cant divide by zero. Pretty much turns it into a one-liner.

Good advice: SourceForge.net: Do not remove parameter names - cpwiki

Originally Posted by iMalc

Yes, and it avoids the need to test for zero denominators first since it cant divide by zero. Pretty much turns it into a one-liner.

Oh one word of warning with this, you may need to enforce the strict policy that the denominator can never be negative, though oviously the numerator can. So 1 / -2 must always be stored as -1 / 2.

Further hint: The same multiplication instead of division change also solves your equality and inequality issues.

having cout statements inside the increment/decrement. (Consider exceptions instead)

O_o

If he wishes his class to consider a denominator of zero to be an error, entirely reasonable, he shouldn't allow an instance of the fraction class to exist which has a zero denominator in the first place.

This check should be in the constructor/stream operators signalling, preferably, with an exception and setting `ios' flags.

Soma

Originally Posted by phantomotap

O_o

If he wishes his class to consider a denominator of zero to be an error, entirely reasonable, he shouldn't allow an instance of the fraction class to exist which has a zero denominator in the first place.

This check should be in the constructor/stream operators signalling, preferably, with an exception and setting `ios' flags.

Soma

Yes that is certainly the better option.