CaesarCipher

#include <ctype.h>
#include <stdio.h>
#include <string.h>
static int decode(char *line) {
  const char *the = "the";
  int i, key = 0;
  while (!strstr(line, the)) {
    for (i = 0; i < strlen(line); i++) {
      if (isupper(line[i]))
        line[i] = (line[i] - 'A' + 1) % 26 + 'A';
      else if (islower(line[i]))
        line[i] = (line[i] - 'a' + 1) % 26 + 'a';
    }
    key++;
  }
  return key;
}
int main(void) {
  char line[BUFSIZ];
  int key;
  printf("cipher text: ");
  fgets(line, BUFSIZ, stdin);
  key = decode(line);
  printf("key: %d\n", key);
  printf("plain text: %s", line);
  return 0;
}