ROT13 (thing)

/*  Rot-13 encoder/decoder in C
 *
 *  This wretched little monstrosity is in the public domain.
 *  A much better solution is to use sed or tr. If you're on 
 *  Windows, go to the GNUish Project and download sed.
 *
 *  As with any simple character translation thing, a 
 *  lookup table would be more efficient, but... come on!
 *
 *  wharfinger  11/5/00
 */

#include <stdio.h>
#include <ctype.h>

int r13( int c );

int main()
{
    int c;

    while ( ( c = getchar() ) != EOF )
        putchar( r13( c ) );

    return 0;
}


int r13( int c )
{
    /*  Okay, it's a nested ternary. I know.
        This should probably be a macro, but macros this complex 
        get on my nerves.  
        'm' is the thirteenth letter of the alphabet.
        I mean, like, in case you didn't know or something.
    */
    return ( isalpha( c ) )
                ? ( ( tolower( c ) > 'm' ) ? ( c - 13 ) : ( c + 13 ) )
                : c;
}