Message-ID: <19971031213656.18761.qmail@hotmail.com>
From: "John Patton" <gimli21 AT hotmail DOT com>
To: djgpp AT delorie DOT com
Cc: nick14 AT erols DOT com
Subject: Re: I need help with a fraction class
Content-Type: text/plain
Date: Fri, 31 Oct 1997 13:36:55 PST
Precedence: bulk

>I've been working on this for a while and I was hoping someone
>could explain these errors.
>
>
>#include "bool.h"
>
>class fractype{
>public:
>    void write() const;
>    float floatequiv();
>    void simplify();
>    fractype operator*(fractype frac2) const;

you should return a reference to fractype... and the function should be 
a *_friend_* of class fractype, not a member:
   friend fractype & operator*(const fractype & frac1,
                               const fractype & frac2);

>    boolean operator==(fractype frac2) const;

Try bool here.  Your implementation is a little 
messed up...  Should be as above:
   friend bool operator==(const fractype & frac1,
                          const fractype & frac2);

>    fractype (int initnumer, int initdenom);

Usually there will also be a default constructor here like:
   fractype(){}

>private:
>    int numer;
>    int denom;
>};
>

you're missing several operators, BTW.  operator=, operator+=, 
operator!=, operator<<, operator>>, ...  to name a few.  when you get 
started on these and need some assistance, let me know...

>
>#include <iostream.h>
>#include <stdlib.h>
>#include "fraction.h"
>
>int GreatestCommonDivisor( int,int);
>
>fractype::fractype(int initnumer, int initdenom)
>{
>numer=initnumer;
>denom=initdenom;
>}
>
>void fraction::write() const;
      ^^^^^^^^               ^
shouldn't it be:             
void fractype::write() const // without the semicolon??

>{
>cout<<numer<<'/'<<denom;
>}
^^^^^^^^^^^^^^^^^^^^^^^^^
also, a better way would be to overload the << operator.

>
>float fractype::floatequiv() 
>{
>return float(numer) / float(denom);
>}
>
>void fractype::simplify()
>{
>int gcd;
>int absnumer= abs(numer);
>
>if (numer==0 || absnumer==1 || denom==1)
>  {
>  return;
>  }
>
>gcd=GreatestCommonDivisor(absnumer, denom);
>if (gcd>1) {
>   numer /= gcd;
>   denom /=gcd;
>  }
>}
>
>fractype fractype::operator*(fractype frac2) const
>{
>int resultnumer = numer * frac2.numer;
>int resultdenom = denom * frac2.denom;
>
>fractype resultfrac(resultnumer, resultdenom);
>resultfrac.simplify();
>return resultfrac;
>}
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Here I will be a little generous and place my own personal version of 
this function...  (remember it's a friend of our class, BTW, so it can 
access our private data!)
You may or may not like it: 

fractype & operator*(const fractype & frac1,
                     const fractype & frac2)
{
    int resultnumer = frac1.numer * frac2.numer;
    int resultdenom = frac1.denom * frac2.denom;

    fractype resultfrac(resultnumer, resultdenom);
    resultfrac.simplify();
    return resultfrac;
}


>
>boolean fractype::operator==(fractype frac2) const
>{
>return (numer==frac2.numer) && (denom==frac2.denom);
>}

Again, I'm feeling generous...
bool operator==(const fractype & frac1,
                const fractype & frac2)
{
    return ((frac1.numer==frac2.numer) && 
            (frac1.denom==frac2.denom));   
}

>
>int GreatestCommonDivisor(int a, int b)
>{
>int temp = a % b;
>while (temp>0) {
>a=b;
>b=temp;
>temp=a%b;
>}
>return b;
>}
>
>

<snip>

>In file included from fraction.cpp:3:
>fraction.h:9: syntax error before `operator'
>fraction.cpp:13: parse error before `::'
>fraction.cpp:50: parse error before `::'
>fraction.cpp:51: no `int fractype::operator ==(class fractype)
>const' member function declared in class `fractype'


I think this should give you a start.  Please correct my mistakes if you 
find any.

Thanks,

John Patton


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