Scanning and Printing short integers

[sackboy127]

Hi,

I need some very basic help with the use of short integers.

I created the following simple program, and it's already giving me errors, probably the second printf is the culprit.

#include "stdafx.h"
#include "conio.h"


int _tmain(int argc, _TCHAR* argv[])
{
    unsigned short int num;
    printf("Please enter a number!\n");
    scanf("%si", &num);

    printf("%si", num);

    _getch();
    return 0;
}

So my question is, what's the proper way of scanning and printing short integers? (I guess it doesn't matter if it's signed or unsigned)

Also, in what interval can a short int store numbers?

Thanks very much!

[Salem]

man page scanf section 3
A brief scan of the manual page would have told you the qualifier was 'h' and not 's'.

[sackboy127]

I'm sorry, didn't know about that page, I'm very new to programming.

I tried it with 'h', but it's still giving me errors. Just to clarify, after declaring a short int variable, do I put '%hi' whenever I want to scan or print it, or only for one of them?

Thanks!

[Barney McGrew]

#include "stdafx.h"
#include "conio.h"

These aren't standard headers, and they aren't particularly useful for what you're trying to accomplish. You need to include the stdio.h header file in order to use printf and scanf.

int _tmain(int argc, _TCHAR* argv[])

I don't know why you define main like this. For most programs, you really only need to use one of the following:

int main(void) { /* ... */ }
int main(int argc, char *argv[]) { /* ... */ }

Which one you use will depend on whether you plan on using the arguments passed by the host environment.

So my question is, what's the proper way of scanning and printing short integers? (I guess it doesn't matter if it's signed or unsigned)

short int a;

if (scanf("%hd", &a) == 1)
    printf("%d\n", a);

For short unsigned int, I suggest using the "%hu" format specifier. Note that the 'h' specifier isn't necessary for printf due to default argument promotions.

Also, in what interval can a short int store numbers?

It varies based on your C implementation. signed short has a minimum guaranteed range of -32767 to +32767 (inclusive), and unsigned short has a minimum guaranteed range of 0 to 65535. You can check their actual ranges by including the header file limits.h and checking the macros USHRT_MAX, SHRT_MAX, and SHRT_MIN. I strongly suggest assuming that each data type has their minimum guaranteed range (as specified by the standard) for the sake of writing portable code.

[iMalc]

The use of StdAfx.h and a main with that signature simply suggest that Visual Studio is being used, but probably an old version given the conio.h.

If the code is giving you errors, then you need to copy and paste them here so that we can see them.

[sackboy127]

Yes, it's Visual Studio 2008.

Now it's working great, thanks very much for all the help, here's the final code:

#include "stdafx.h"
#include "conio.h"


int _tmain(int argc, _TCHAR* argv[])
{
    unsigned short int num;
    printf("Please enter a number!\n");
    scanf("%hi", &num);

    printf("%hi", num);

    _getch();
    return 0;
}

I don't know why my teacher told me that there's no problem with using %si.

[Salem]

    scanf("%si", &num);
    printf("%si", &num);

Would appear to 'work' for rather perverse reasons, because %s is actually for strings, not 'short' integers. If you only typed in a single letter, you'd probably be OK, but anything else would be a buffer overflow.

printf/scanf don't care that you got the type of pointer wrong (pointer to int vs pointer to char). All they see is "pointer" and off they go, assuming you did the right thing by passing a char pointer.
The GCC compiler will actually check printf/scanf calls, so this useful if you have a choice to use it.

A short int is typically 2 bytes, so there isn't room for a long string, and trying it would result in a buffer overflow (and the resulting weird behaviour ranging from "it works" to "where are my install disks" and "where's that smoke coming from!?").

> I don't know why my teacher told me that there's no problem with using %si.
Teachers and books can be wrong (and many are). Some however throw in the occasional mistake just to see who's paying attention.
Never rely too heavily on a single source without doing some cross-checking.