matrices

Discussion in 'C++' started by tommy, Dec 3, 2004.

  1. tommy

    tommy Guest

    Hello everyone,

    I'm trying to write a program which will be adding and subtracting
    two matrices. I've already written some code but there are a few problems.

    1) During compilation I get this warning:
    mt.cpp 17: temporary used for parameter 1 in call to: istream: operator >>
    (int &)
    2) When I'm trying to show results of addition and subtraction two matrices
    I get some strange really big unexpected numbers.

    The source code is bellow. I use Borland C++ v3.1
    ----------
    def.h
    ----------
    #ifndef _DEF_H_
    #define _DEF_H_

    #include <iostream.h>
    #include <conio.h>
    #include "mt.h"

    #endif
    ---------
    mt.h
    ---------
    #ifndef _MT_H_
    #define _MT_H_

    class Mt { /* multidimensional table */
    public:
    Mt() ;
    void fill() ;
    friend void operator+(Mt &,Mt &) ;
    friend void operator-(Mt &,Mt &) ;
    private:
    int values[5][5] ;
    const int firstcolumn ; /* number of first column in table
    */
    const int firstline ; /* number of first line in table */
    int column ;
    int line ;
    const int nc ; /* number of columns */
    const int nl ; /* number of lines */
    } ;

    #endif
    --------
    main.cpp
    --------
    #include "def.h"

    int main(int , char *[]) /* argument counter, argument vector */
    {
    clrscr() ;

    Mt m1, m2 ;
    m1.fill() ;
    m2.fill() ;

    m1 + m2 ;
    m1 - m2 ;

    getch() ;
    return 0 ;
    }
    -------
    and mt.cpp
    -------
    #include "def.h"

    Mt::Mt() : firstcolumn(0), firstline(0), nc(5), nl(5)
    {
    ; /* do nothing */
    }

    void Mt::fill()
    {
    column = firstcolumn ;

    while( column < nc )
    {
    for(line = firstline ; line < nl ; line++)
    {
    cout << "i= " << column << " j= " ;
    cin >> values[column][line] ;
    }

    column++ ;
    }
    }

    void operator+(Mt &first, Mt &second)
    {
    int sum[5][5] ;

    // Let's make some addition of these two tables

    int column = 0 ;
    int line = 0 ;

    cout << "\nAddition: \n" ;

    while( column < 5 )
    {
    for(line = 0 ; line < 5 ; line++)
    sum[column][line] = first.values[column][line] +
    second.values[column][line] ;

    column++ ;
    }

    column = 0 ;

    while( column < 5 )
    {
    if ( column <= 5 - 1)
    cout << "\n" ;

    for(line = 0 ; line < 5 ; line++)
    cout << sum[line][column] << " " ;

    column++ ;
    }
    cout << "\n\n" ;
    }

    void operator-(Mt &first, Mt &second)
    {
    int sum2[5][5] ;

    // Let's make some addition of these two tables

    int column = 0 ;
    int line = 0 ;

    cout << "\nSubtraction :\n" ;

    while( column < 5 )
    {
    for(line = 0 ; line < 5 ; line++)
    sum2[column][line] = first.values[column][line] -
    second.values[column][line] ;

    column++ ;
    }

    column = 0 ;

    while( column < 5 )
    {
    if ( column <= 5 - 1)
    cout << "\n" ;

    for(line = 0 ; line < 5 ; line++)
    cout << sum2[line][column] << " " ;

    column++ ;
    }
    cout << "\n\n" ;
    }
    --------
    Any help will be appreciate,
    Regards
    tommy
     
    tommy, Dec 3, 2004
    #1
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  2. tommy wrote:
    > I'm trying to write a program which will be adding and subtracting
    > two matrices. I've already written some code but there are a few problems.
    >
    > 1) During compilation I get this warning:
    > mt.cpp 17: temporary used for parameter 1 in call to: istream: operator >>
    > (int &)


    Really? The only 'cin' I see is in the 'fill' function and it doesn't
    look like a use of a temporary to me... Hard to say. Your code is non-
    standard and I don't have BC++ v3.1 to verify your claim.

    > 2) When I'm trying to show results of addition and subtraction two matrices
    > I get some strange really big unexpected numbers.
    >
    > The source code is bellow. I use Borland C++ v3.1


    That's about as old a compiler as one can find still in use. Perhaps you
    should consider at least upgrading to the [free] v5.5...

    Now, about the code...

    > ----------
    > def.h
    > ----------
    > #ifndef _DEF_H_
    > #define _DEF_H_


    Names with leading underscore followed by a capital letter are reserved by
    the implementation. There is no need for you to have that fancy leading
    underscore here. Be simple.

    >
    > #include <iostream.h>


    There is no standard header <iostream.h>. Use <iostream> and make sure to
    change your code appropriately.

    > #include <conio.h>


    There is no standard header <conio.h>. Whatever may arise from using it
    is not guaranteed by the language.

    > #include "mt.h"
    >
    > #endif
    > ---------
    > mt.h
    > ---------
    > #ifndef _MT_H_
    > #define _MT_H_
    >
    > class Mt { /* multidimensional table */


    Misleading comment. It's really has a _two_ dimensional "table" and of
    very specific size.

    > public:
    > Mt() ;
    > void fill() ;
    > friend void operator+(Mt &,Mt &) ;
    > friend void operator-(Mt &,Mt &) ;


    Seems like two operators. Good. But why do they return 'void'? Do you
    not want some result from those operations recorded?

    Change those to
    friend Mt operator+(Mt const&, Mt const&);
    friend Mt operator-(Mt const&, Mt const&);

    And add
    void print() const; // think of how you'd implement it.

    > private:
    > int values[5][5] ;
    > const int firstcolumn ; /* number of first column in table
    > */
    > const int firstline ; /* number of first line in table */
    > int column ;
    > int line ;


    These two members above don't have any comment next to them. What are
    they for?

    > const int nc ; /* number of columns */
    > const int nl ; /* number of lines */
    > } ;
    >
    > #endif
    > --------
    > main.cpp
    > --------
    > #include "def.h"


    This is a rather bad practice if you ask me. It is much better to
    explicitly include all headers than do it indirectly through another
    header. Doing it indirectly does NOT help improve compilation speed
    and only adds confusion when one is looking at the 'main.cpp' module.

    >
    > int main(int , char *[]) /* argument counter, argument vector */
    > {
    > clrscr() ;


    Non-standard function. Try to avoid those until your program works.

    >
    > Mt m1, m2 ;
    > m1.fill() ;
    > m2.fill() ;
    >
    > m1 + m2 ;
    > m1 - m2 ;


    These two statements above are very strange. Imagine I'd write

    int i1, i2;
    i1 = 1;
    i2 = 2;
    i1 + i2;

    What does the addition do? Nothing. It adds two values and the sum is
    simply thrown away. That's what the m1+m2; looks to me.

    Read a good book about operator overloading. Find a copy of "Effective
    C++" by Scott Meyers, you seem to be in desperate need of reading it.

    The code in 'main' should be changed to

    Mt msum = m1 + m2;
    Mt mdiff = m1 - m2;
    .. // somehow output the contents of 'msum' and 'mdiff'

    >
    > getch() ;
    > return 0 ;
    > }
    > -------
    > and mt.cpp
    > -------
    > #include "def.h"


    Again, avoid using those "collection" headers. Be explicit.

    >
    > Mt::Mt() : firstcolumn(0), firstline(0), nc(5), nl(5)


    Kudos! That's a very rare thing to see a novice who uses initialiser
    lists instead of assignments. Good job!

    > {
    > ; /* do nothing */


    You don't need a semicolon here to do nothing. You may leave the comment
    in if you want but many would understand that

    {
    }

    does nothing.

    > }
    >
    > void Mt::fill()
    > {
    > column = firstcolumn ;
    >
    > while( column < nc )
    > {
    > for(line = firstline ; line < nl ; line++)


    Rather strange choice of loop controlling statements. Why not
    both 'while' or both 'for'?

    > {
    > cout << "i= " << column << " j= " ;


    Prints

    i= <number> j=

    Did you forget to output 'line'?

    > cin >> values[column][line] ;
    > }
    >
    > column++ ;
    > }
    > }
    >
    > void operator+(Mt &first, Mt &second)


    Well, if you read the "Effective C++", you'll know how you should declare
    the addition operator:

    Mt operator +(Mt const &first, Mt const &second)

    > {
    > int sum[5][5] ;


    This should probably be

    Mt sum;

    >
    > // Let's make some addition of these two tables
    >
    > int column = 0 ;
    > int line = 0 ;
    >
    > cout << "\nAddition: \n" ;


    You might want to leave this in for debugging purposes, but really your
    addition operator shouldn't be telling everybody it's doing its job.

    >
    > while( column < 5 )
    > {
    > for(line = 0 ; line < 5 ; line++)
    > sum[column][line] = first.values[column][line] +
    > second.values[column][line] ;


    Since I recommend changing 'sum' to be of type Mt, this should become

    sum.values[column][line] = ...

    >
    > column++ ;
    > }
    >
    > column = 0 ;
    >
    > while( column < 5 )
    > {
    > if ( column <= 5 - 1)
    > cout << "\n" ;
    >
    > for(line = 0 ; line < 5 ; line++)
    > cout << sum[line][column] << " " ;
    >
    > column++ ;
    > }
    > cout << "\n\n" ;


    You should consider creating a special _separate_ function for outputting
    the result (an Mt object)

    And, of course, since we changed the return value type, you need

    return sum;

    here.

    > }
    >
    > void operator-(Mt &first, Mt &second)
    > [...]


    Same notes as with the operator +.

    All in all, a very good effort! Now, get a copy of "Effective C++" and
    consume it.

    Victor
     
    Victor Bazarov, Dec 3, 2004
    #2
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  3. tommy

    Rade Guest

    "tommy" <> wrote in message
    news:a72dx16hlcpf.j4cd6fuzgc4d$...
    > Hello everyone,
    >
    > I'm trying to write a program which will be adding and subtracting
    > two matrices. I've already written some code but there are a few problems.
    >
    > 1) During compilation I get this warning:
    > mt.cpp 17: temporary used for parameter 1 in call to: istream: operator >>
    > (int &)
    > 2) When I'm trying to show results of addition and subtraction two
    > matrices
    > I get some strange really big unexpected numbers.
    >
    > The source code is bellow. I use Borland C++ v3.1


    [cut]

    First of all, I have used this compiler (and the accompanying IDE, debugger
    and so on) many years ago. The debugger was a decent one for these years...
    So I expect you will be able to go step by step through your code until you
    find the bug.

    IIRC, if BC++ 3.1 reports such a warning, it actually means what is stated
    in the warning, i.e. that the integer is read to a temporary, which is then
    assigned to your 'values' array. Honestly, I don't see why this happens, but
    I can see no harm if this happens. However, please check this by setting a
    breakpoint at this line, going just one step and checking if the 'values'
    array actually contains what you have typed.

    Having this sorted out, the problem (2) may be a consequence of mixing rows
    and columns. Generally, your first index is a column, and the second one is
    a row, but it is opposite when you print. More counterintuitively, you print
    horizontal columns and vertical lines (?!).

    Regards,
    Rade

    P.S. A general comment... actually many people are posting questions like
    "Why my program doesn't work ?" (often with lots of code). What I can't
    understand is why it is so hard to learn a couple of basic debugging steps -
    step into a function, step out of the function, watch the variable, set a
    breakpoint. Not a rocket science. Even if they work on a platform where they
    don't have debugger, it is easy to add some additional printouts at critical
    places in the code, and later look at the results. This way, beginner finds
    his/her own bug, instead of posting a question and hoping that somebody else
    will find it.
     
    Rade, Dec 3, 2004
    #3
  4. Rade wrote:
    > [...]
    > P.S. A general comment... actually many people are posting questions like
    > "Why my program doesn't work ?" (often with lots of code). What I can't
    > understand is why it is so hard to learn a couple of basic debugging steps -
    > step into a function, step out of the function, watch the variable, set a
    > breakpoint. Not a rocket science. Even if they work on a platform where they
    > don't have debugger, it is easy to add some additional printouts at critical
    > places in the code, and later look at the results. This way, beginner finds
    > his/her own bug, instead of posting a question and hoping that somebody else
    > will find it.


    Couldn't you answer your own questions here? It's so much easier when the
    entire planet is working for you instead of sitting there typing cout and
    printf or stepping through the code that you are already sick of because
    you have been mucking in it for the past several hours...

    A while back in the old country when I learned to program, there was no
    Usenet. We had to walk to school barefoot in the snow twenty miles all
    uphill. We ate tin cans for breakfast and smoked cow manure to keep us
    warm... And there were no debuggers and the computers were so old we had
    to chop wood before we could boot them up, so printouts were out of the
    question because most of the paper we usually spent on kindling the wood
    or making cow manure joints...

    Nowadays, paper is cheap here, besides, the debuggers are visual. And,
    with Internet developing and spreading around the globe, there is no need
    for the beginners to learn debugging or writing programs on a chalk- or
    white-board first. Forgeddaboudid!

    V
     
    Victor Bazarov, Dec 3, 2004
    #4
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