text: #include <ctype.h>
  #include <cs50.h>
  #include <stdio.h>
  #include <string.h>
  #include <stdlib.h>
  
  int main(int argumentCount, string argumentList[])
  {
      if (argumentCount != 2)
      {
          printf("Usage: ./caesar key");
          return 1;
      }
      //put key into a varable and convert it to integer
      int key = atoi(argumentList[1]);
  
      //check if int is non negative
      if (key < 0)
      {
          printf("Usage: ./caesar key");
          return 1;
      }
      else
      {
          //get plaintext from user
          string plaintext = get_string("plaintext: ");
          printf("ciphertext: ");
          for (int i = 0, leng = strlen(plaintext); i < leng; i++)
          {
              //chequear si la letra es uppercase or lowercase y convertir
              if islower(plaintext[i])
              {
                  printf("%c", (((plaintext[i] + key) - 97) % 26) + 97);
              }
              else if isupper(plaintext[i])
              {
                  printf("%c", (((plaintext[i] + key) - 65) % 26) + 65);
              }
              else
              {
                  printf("%c", plaintext[i]);
              }
          }
          printf("\n");
          return 0;
      }
  }
  