/*****************************************************************************
*                                                                            *
*               ==============================================               *
*                                                                            *
*****************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define usage() fprintf(stderr, "usage: %s inputfile outputfile key\n", progammname)


/*****************************************************************************
*                                                                            *
*  --------------------------------- main ---------------------------------  *
*                                                                            *
*****************************************************************************/

int main(int argc, char *argv[]) {

/*Programmname merken*/
char *progammname = argv[0];
FILE *inputfile;
FILE *outputfile;
int anz_gelesen;
unsigned long key;
unsigned long gelesen;
			
/*Argumentverarbeitung, */
/*falls filename angegeben wird in diesen geschrieben, sonst auf stdout*/
if (argc == 4)
{
	inputfile = fopen(argv[1],"r");

	if(inputfile == NULL)
	{
		fprintf(stderr,"Fehler beim Oeffnen der Datei %s zum Lesen.\n", argv[1]);		
		usage();
		return -1;
	}
	else
	{
		outputfile = fopen(argv[2],"w");

		if(outputfile == NULL)
		{
			fclose(inputfile);
			fprintf(stderr,"Fehler beim Oeffnen der Datei %s zum Schreiben.\n", argv[2]);		
			usage();
			return -1;
		}	
	}
	sscanf(argv[3], "%lu", &key);	
	fprintf(stdout, "Key: %ld\n", key);
}
else
{
	usage();
	return -1;
}

while ((anz_gelesen = fread((void*)&gelesen, 1, 4, inputfile)) > 0)
{	
	gelesen = gelesen ^ key;		
	fwrite((void*)&gelesen, 1, anz_gelesen,outputfile);	
	gelesen = 0;
	anz_gelesen = 0;
}

fclose(inputfile);
fclose(outputfile);
return 0;

}