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

#define MAX_FILE_NAME_LEN 80

int main(int argc, char **argv)
{
char source_file_name[MAX_FILE_NAME_LEN + 1];
char dest_file_name[L_tmpnam];
int key, ch;
FILE *fsource, *fdest;

if (argc != 2) {
printf("sifrelenecek dosyanin ismini giriniz : ");
gets(source_file_name); 
printf("anahtar degerini giriniz : ");
scanf("%d", &key);
}
else {
strcpy(source_file_name, argv[1]);
key = atoi(argv[2]);
}

tmpnam(dest_file_name);

fsource = fopen(source_file_name, "rb");
if (fsource == NULL) {
fprintf(stderr, "%s dosyasi acilamiyor!\n", source_file_name);
exit(EXIT_FAILURE);
}

fdest = fopen(dest_file_name, "wb");
if (fdest == NULL) {
fprintf(stderr, "%s dosyasi yaratilamiyor!\n", source_file_name);
fclose(fsource);
exit(EXIT_FAILURE);
}

srand(key);

while ((ch = fgetc(fsource)) != EOF)
fputc(ch ^ rand(), fdest);

fclose(fsource);
fclose(fdest);

remove(source_file_name);
rename(dest_file_name, source_file_name);

return 0;
}