CS50 week 2/week 8 vigenere

vigenere.c

/**
* CS50 week 2 vigenere
*/

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

int main(int argc, string argv[])
{
    // make sure user gives secret key from command line 
    if (argc!=2)
    {
        printf("missing command-line argument\n");
        return 1;
    }
    else
    {
        //check if characters in argv[1] are alphabedic
        for (int l=0, s=strlen(argv[1]); l<s; l++)
        {
            if(!isalpha(argv[1][l]))
            {
                printf("key word can contain only alphabetic characters\n");
                return 1;
            }
        }

        printf("plaintext:");
        string plaintext=get_string();
    
        if (plaintext!=NULL&&argv[1]!=NULL)
     {
        printf("ciphertext:");
       
        //iterate over the characters in the plaintext one at a time and get access to consecutive characters of argv[1] key
        for (int i=0, n=strlen(plaintext), k=0; i<n; i++)
        {   
            int cyphertext;
            //check if [i] character is an alphabetic character and uppercase
            if (isalpha(plaintext[i])&&isupper(plaintext[i]))
            {
                //find alphabetic index of uppercase character in plaintext
                int alph_index=plaintext[i]%65;
                
                //get access to j character in agrv[1] and find it's alphabetic index
                int j=k%(strlen(argv[1]));
                int alph_index_argv=toupper(argv[1][j])%65;
                
                //find and print corresponding character in ciphertext in ASCII in uppercase
                cyphertext=65+(alph_index+alph_index_argv)%26;
                
                printf("%c", cyphertext);
                k++;
            }    
             else
             {
                //check if [i] character is alphabetic character and lowercase
                 if (isalpha(plaintext[i])&&islower(plaintext[i]))
                 {
                     //find alphabetic index of lowercase character in plaintext
                     int alph_index=plaintext[i]%97;
                     
                     //get access to j character in agrv[1] and find it's alphabetic index
                     int j=k%(strlen(argv[1]));
                     int alph_index_argv=toupper(argv[1][j])%65;
                     
                     //find and print corresponding character in ciphertext in ASCII in lowercase
                     cyphertext=97+(alph_index+alph_index_argv)%26;
                     printf("%c", cyphertext);
                     k++;
                 }
                 else 
                 {
                     //print [i] character if it is not alphabetic character
                     printf("%c", plaintext [i]);
                 }
             
             }
        }     
    
    printf("\n");
    return 0;
    }
    }
}

vigenere.py

#program that encrypts messages using Vigenère’s cipher


def main():
     import sys
     import cs50

     # make sure user gives secret key from command line
     if len(sys.argv) != 2:
         print("missing command-line argument")
         sys.exit(1)
     else:
         key = str(sys.argv[1])
         #check if characters in argv[1] are alphabetic
         for char in key:
             if not str.isalpha(char):
                 print("key word can contain only alphabetic characters")
                 sys.exit(1)

         #get plaintext from a user
         print("plaintext:", end = "")
         plaintext = cs50.get_string()

         if plaintext != None and str(sys.argv[1]) != None:
             print("ciphertext:", end="")

             k = 0
             for char in plaintext:
                 #check if char character is an alphabetic character and uppercase
                 if str.isalpha(char) and str.isupper(char):
                     #//find alphabetical index of uppercase character in plaintext
                     alph_index = ord(char)%65

                     #//get access to j-th character in agrv[1] and find it's alphabetic index
                     j = k%(len(sys.argv[1]))
                     alph_index_argv = ord(str.upper(sys.argv[1][j]))%65

                     #//find and print corresponding character in ciphertext
                     ciphertext = chr(65 + (alph_index+alph_index_argv)%26)

                     print(ciphertext, end = "")
                     k += 1

                     #check if char character is alphabetic character and lowercase
                 elif str.isalpha(char) and str.islower(char):

                     #find alphabetic index of lowercase character in plaintext
                     alph_index = ord(char)%97

                     #get access to j-th character in agrv[1] and find it's alphabetical index
                     j = k%(len(sys.argv[1]))
                     alph_index_argv = ord(str.upper(sys.argv[1][j]))%65

                     #find and print corresponding character in ciphertext in ASCII in lowercase
                     ciphertext = chr(97 + (alph_index + alph_index_argv)%26)

                     print(ciphertext, end = "")
                     k += 1
                 else:
                     #print char character if it is not alphabetic character
                     print(char, end = "")

             print()
             exit(0)

if __name__ == "__main__":
    main()