Thread: Hex scanf input and printf output.

I am trying to write a program using unsigned char, that prompts the user to enter a two-digit hex value, then displays the value. Can anyone point me in the right direction? Thanks This is what I have so far.swapnibbles.c Also.

Code:

#include <stdio.h>


unsigned char swapnibbles(unsigned char data)
{
    if
        ((data < 0x00) || (data > 0xFF) )
            printf ("\nInvalid Entry\n");
}


unsigned char data (void)
{
    unsigned char  data;
    scanf ("%0x", &data);
    printf ("0x", data);


    return data;
}


char main (void)


{
    data ();


    return 0;
}

Line 15 should read ... scanf("%hhx", &data);
Line 16 should read ... printf("%x", data);

Also your test in lines 6 through 8 does nothing since it's impossible for an unsigned char value to hold numbers less than 0 or greater than 255.

Thanks Tater, got it! What does the %hhx specifically do? I couldn't find that in my book?

Originally Posted by et3ruiz

Thanks Tater, got it! What does the %hhx specifically do? I couldn't find that in my book?

Ok, something to learn real quick... Programming textbooks are not complete references to the C language or it's libraries. They are enough to get you started and always the assumption is that you will continue learning after.

Your compiler should have documentation for it's keywords, libraries, toolchain, etc. If you don't have it ... get it.
If your compiler doesn't have it... get one that does.

The first thing you will discover is that your textbooks gave you about 5% of the full disclosure...

At least half of a programmer's work is "looking stuff up" which is exactly what you need to do with things like the format strings in printf() and scanf()...
Even if you *think* you know, you should still look it up to be certain (which is exactly what I did when answering your question).