Thread: Can you help me with my Vignere encryption algorithm?

There are quite a few problems:

• #include <typec.h> probably should have been #include <ctype.h>
• strlen(argv) does not make sense. argv is conceptually an array of strings. Perhaps you wanted strlen(argv[1]) instead, but you should check the value of argc before accessing that.
• This line is syntactically incorrect:
  
  Code:

  int k[sizeofa] = argv[];

  It looks like you don't even need it: you can check argc to determine if the user entered too many arguments, and you can pass argv[1] to encryptor.
• You should not use gets because it is inherently vulnerable to buffer overflow. fgets is a possible alternative, though keep in mind that fgets retains the newline entered if there is space.
• This looks like a common mistake:
  
  Code:

  if (j = m - 1)

  You probably intended to use == instead of = here
• You need to indent your code properly. This is especially important in the encryptor function because it helps to show the reader the structure of the code, e.g.,
  
  Code:

  void encryptor(char k[], char string[]) {
   
  for (int i = 0, n = strlen(string); i < n; i++)
      for (int j = 0, m = strlen(k); j < m; j++)
      {
          if (isalpha(string[i]) {
              string[i] = string[i] + k[j];
              printf("%c", string[i])
          }
          else {
              printf("%c", string[i]);
              j--;
          }
  
          if (j = m - 1) 
              j = 0;
      }
  }

  Incidentally, since you are not changing the contents of k, k should have been declared as const char k[] instead. Also, it would be better to name it key instead of k.