#include <stdio.h>

void main(int argc, char * argv[])
{
	FILE * infile;
	FILE * outfile;
	char byte;
  int offset;

	if(argc!=5)
	{
		printf("Sintassi: CRYPT nomefile-input nomefile-output operation offset\n");
		return;
	}

	infile=fopen(argv[1], "r");
	if(infile==NULL)
	{
		printf("Impossibile aprire in lettura il file [%s]\n", argv[1]);
		return;
	}

	outfile=fopen(argv[2], "w");
	if(outfile==NULL)
	{
		printf("Impossibile aprire in scrittura il file [%s]\n", argv[2]);
		return;
	}

  offset = atoi(argv[4]);

	while(!feof(infile))
	{
		byte=fgetc(infile);   /* byte=getc(); */

		if(byte == EOF)
			break;

    if(argv[3][0]=='c')
    	byte+=offset;
    else if(argv[3][0]=='d')
      byte-=offset;

		fputc(byte, outfile);

	}
	fclose(infile);
	fclose(outfile);
}