#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <string.h>
int main(int argc , string argv[])
{
   if (argc == 2  )
   {
        int  key_start_over = 0 , length_of_key = strlen(argv[1]);
        string key = argv[1];

         for (int i = 0; i < length_of_key ; i ++)
       {
          while (key[i] >= '0' && key[i]<= '9') /* accept no numbers at the key */
          {
              printf("Usage: %s k\n",argv[0]);
              return 1 ;
          }
       }
          printf("plaintext:");
          string c = get_string(); /* the plaintext */
          printf("ciphertext:");
          if (c!= NULL)
          {
          for (int i2 = 0 , length_c = strlen(c) ; i2 < length_c ; i2++)
          {
              if (isupper(key[key_start_over]))
              {
                  key[key_start_over] -= 'A';
                  /* if the character is capital take 65 from it // ex: if char is 'A' that means character equals 0 */
              }
              if (islower(key[key_start_over]))
              {
                  key[key_start_over] -= 'a';
                  /* if the character is small take 97 from it // ex: if char is 'b' that means character equals 1 */
              }

              if (isalpha (c[i2]) && c[i2] != ' ') /* if the character is a letter and its not a "space" */
              {
                  if (isupper(c[i2]) && c[i2] + key[key_start_over] > 'Z'  )
                  { /*if the character is capital and if the character + the key is bigger than Z minus 26 which means start from the beginning */
                      printf("%c",((c[i2]+key[key_start_over]) - 26) );
                  }
                  else if(isupper(c[i2]) && (c[i2] + key[key_start_over] ) <= 'Z'  )
                  {
                     printf("%c",(c[i2]+key[key_start_over]));
                  }
                  if (islower(c[i2]) && c[i2] + key[key_start_over] > 'z')
                  { /*if the character is small and if the character + the key is bigger than z minus 26 which means start from the beginning */
                      printf("%c",((c[i2] + key[key_start_over]) - 26));
                  }
                  else if (islower(c[i2]) &&( c[i2] + key[key_start_over]) <= 'z')
                  {
                       printf("%c",(c[i2] + key[key_start_over]));
                  }
                  key_start_over ++ ;
                  if (key_start_over >= length_of_key)
                  { /* if the key letter ends start over */
                  key_start_over = 0 ;
                  }
              }
              else
              { /* if the character is a space print it */
                  printf("%c",c[i2]);
              }
          }
   }
   printf("\n");
   }
   else
   { // if the command-line-argument is less or bigger than 2 print this error message  //
       printf("Usage: %s k\n",argv[0]);
       return 1 ;
   }
}