#include <stdio.h>

main()
{
 FILE *Fin, *Fout;
 char p, c, K[20];
 int n, i; 
 
 Fin = fopen("plain.txt", "r");
 Fout = fopen("cipher.txt", "w");
 
 printf("Ketikkan kata kunci : "); gets( K);

 n = strlen(K);
 i = 0;
 while (!feof(Fin)) 
 {
  fscanf(Fin, "%c", &p);
  c = p ^ K[i];
  fprintf(Fout, "%c", c);  
  i++; if (i>n) i =0;
 }
 
 fclose(Fin);
 fclose(Fout); 
}