Re: [Dev-C++] short integer problem

[<jar...@ig...>]

On  6 Jun, rchavez wrote:
> Hi,
> 
> While trying a problem from my text 'A Book on C' I ran into some strange
> behavior for short integers.  If I use integers, the program below reads
> them in & performs the arithmetic correctly.  But if I change line 3 so the
> variables are of type short, the value of x is always 0 !!
> 
> I've played with it a lot but can't find the problem.  Any help would be
> appreciated.  Also, notice that the scanf for var ss at the bottom always
> works.  It's not a gcc bug since I get the same behavior on a unix compiler.
> 
> Rob
> 
> /** Math on Short Integers **/
> 
> main()
> {
>    short x,y, entries=2;     /* declared as int program works as expected */
>    short ss;
>    printf("\n sizeof(short): %d",sizeof(short));
>    printf("\n2 to the 15: %d\n\n",128*128*2);
>    printf("\n Enter 2 int values: \n");
>    entries=scanf("%d",&x);
====================^^   ^
Since  x  is of type  short int you MUST you the input format
%hd . If you write  %d  scanf inputs  4 bytes and thus overwrites the
2 bytes in storage following  x  .
Since scanf  use a variable parameter list type checking is disabled.
One more reason to avoid  the  C  input/output system.
In C++ the input operator '>>' has no such problems.
The same in the scanf calls below.

>    entries +=scanf("%d",&y);
>    printf("\n x= %d   y= %d",x,y);
> 
>    while (entries == 2) {
>        printf("\n x= %d   y= %d",x,y);
>        printf("\nX+Y = %d",x+y);
>        printf("\nX-Y = %d",x-y);
>        printf("\nX*Y = %d",x*y);
>        printf("\nX/Y = %d",x/y);
>        printf("\nx %c y = %d\n",'\045',x%y);
> 
>        ss = 64000;
>        printf("\nEnter a short int");
>        scanf("%d",&ss);
>        printf("\n Another try on a short int gives: %d",ss);
>        printf("\n Enter 2 int values: ");
>        entries=scanf("%d%d",&x,&y);
>    }
> 
>    printf("\n\n");
>    system("PAUSE");
>       return 0;
> }
> 



-- 
Helmut Jarausch

Lehrstuhl fuer Numerische Mathematik
Institute of Technology, RWTH Aachen
D 52056 Aachen, Germany