KANDEL910

#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>

int main(int argc, string argv[])
{

    string k = argv[1];
    //k will be the key

//this for loop checks if all of the characters are in the alphabet
int l = strlen(k);
    for (int i = 0; i < l; i++)
    {
        if (isupper(k[i]) || islower(k[i]))
        {
        }
        else
        {
             printf ("error!\n");
              return 1;
        }
    }
    //this if checks if argc equals 2 which means the user has given a correct key
    if (argc != 2)
    {
    printf ("error!\n");
    return 1;
    }

    string s = get_string("plaintext:");

    for (int j = 0; j < strlen(s); j++)
    {
       int m = j % l;
        if (isupper(s[j]))
       {
        k[m] -= 65;
        s[j] += k[m];
          if (s[j] > 90)
          {
             s[j] -= 26;
          }
       }
       if (islower(s[j]))
       {
           k[m] -= 97;
           s[j] = s[j] + k[m] - 26;
            if (s[j] < 97)
            {
                s[j] += 26;
            }
       }
    }
    printf("ciphertext:%s\n", s);
}