c - Vigenere cypher program error for cs50 -

i'm writing vigenere cypher program in c cs50 , have working perfectly. error when encryption wraps around output ? symbol in white circle.

below code;

#include <cs50.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <ctype.h>  int main(int argc, string argv[]) { char a; char letter; char cryptletter; char passletter; string message; int messcount = 0;  if(argc != 2) {     printf("command line must contain 1 passphrase\n");     return 1; }  for(int i=0; < strlen(argv[1]); i++) {     = argv[1][i];      if(isalpha(a) == 0)     {         printf("encryption keyphrase must contain alphabetic characters\n");         return 1;     } }   message = getstring();   (int j = 0; j < strlen(message); j++) {     letter = message[j];      if(passletter < 91 && passletter > 64)     {         passletter = passletter + 32;     }      if(isupper(letter) != 0) //if uppercase 65-90     {         passletter = argv[1][messcount];         cryptletter = passletter + letter - 97;          if(cryptletter > 90)         {             cryptletter = cryptletter - 25;         }          printf("%c", cryptletter);         messcount++;     }      if(islower(letter) != 0) //if lowercase 97-122     {         passletter = argv[1][messcount];         cryptletter = passletter + letter - 97;          if(cryptletter > 122)         {             cryptletter = cryptletter - 25;         }          printf("%c", cryptletter);         messcount++;     }       if(messcount > strlen(argv[1])-1)     {         messcount = 0;     }      if (isalpha(letter) == 0)     {         printf("%c", letter);     } }  printf("\n"); } 

any appreciated, having similar problem caesar cypher. thanks

here:

if(passletter < 91 && passletter > 64) 

passletter uninitialized