/*
Program: CODE.C
Author : Kim Moser
Date   : 02/16/89
System : IBM PC / Borland Turbo-C 2.0
Descrip: Encodes stdin and sends it to stdout

Usage  : CODE [+|-]<key>[+|-]

	 + or - before key means add or subtract key to/from data
	 + or - after key means add or subtract data to/from key
*/

#include <stdio.h>
#include <stdlib.h>  /* exit() */
#include <io.h>  /* setmode() */
#include <fcntl.h>  /* O_BINARY */
#include <ctype.h>

void usage(void)
{
	fputs( "CODE v1.0 09/30/89  Copyright (C) 1989  Kim Moser  All Rights Reserved\n", stderr );
	fputs( "CODE: Encodes data from stdin, writes encoded form to stdout\n", stderr );
	fputs( "Usage: CODE [+|-]key[+|-]\n", stderr );
	fputs( "  '+' or '-' before key means add key to or subtract key from data\n", stderr );
	fputs( "  '+' or '-' after key means add data to or subtract data from key\n", stderr );
	exit(-11);
}

void main(argc, argv)
int argc;
char **argv;
{
	int pre=0, post=0;  /* -1=subtract, 0=no op, 1=add */
	unsigned int key;
	int ch;
	int i;

	if (argc!=2) usage();
	switch(argv[1][0]) {
		case '+':
			pre=1;
			break;
		case '-':
			pre=-1;
			break;
	}

	if (!argv[1][pre?1:0]) usage();  /* Nothing left to parse */
	if (!isdigit(argv[1][pre?1:0])) usage();  /* No key follows */
	if (!sscanf(&argv[1][pre?1:0],"%u",&key)) usage();

	/* Starting at 2nd char, find first non-digit (or EOS): */
	for (i=1; isdigit(argv[1][i]) && argv[1][i]; i++);

	/* Find first non-digit (or EOS): */
	while ( isdigit(argv[1][i]) && argv[1][i] )
		i++;

	switch(argv[1][i]) {
		case '+':
			post=1;
			break;
		case '-':
			post=-1;
			break;
		case '\0':  /* Do nothing */
			break;
		otherwise:
			usage();
	}

	if (!pre && !post) usage();  /* Only key specified */

	fprintf( stderr, "Formula: %s%s%u%s%s\n", (pre?"Data":""),
	  (pre<0?" - ":(pre>0?" + ":"")), key,
	  (post<0?" -":(post>0?" +":"")), (post?" data":"") );

	if ( setmode(fileno(stdin),O_BINARY) ) {
		fputs("Unable to set stdin to binary.\n", stderr);
		exit(-1);
	}
	if ( setmode(fileno(stdout),O_BINARY) ) {
		fputs("Unable to set stdout to binary.\n", stderr);
		exit(-1);
	}

	while ((ch=getchar())!=EOF) {
		if (pre<0) ch-=key;
		else if (pre>0) ch+=key;

		if (post<0) ch = key-ch;
		else if (post>0) ch = key+ch;

		putchar(ch);
	}
}