caesar encoding

caesar.c

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

char secret[] = "MY SECRET STRING";

int main(int argc, char *argv[]) {
  char encoded[strlen(secret)];
  int i;

  printf("Shifting '%s' by %d:\n", secret, atoi(argv[1]));

  for(i=0; i < strlen(secret); i++) {
    encoded[i] =  secret[i] + atoi(argv[1]);
  }
  printf("%s\n",encoded);

  return 0;
}