CS50 week2/week8 caesar

caesar.c

/**
* CS50 week2 caesar
*/

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

int main(int argc, string argv[])
{
    int key;
    
    // make sure a user gives a secret key from command line 
    if (argc!=2)
    {
        printf("missing command-line argument\n");
        return 1;
    }
    else
    {
    //convert a string from argv[] to an integer (key)
    key=atoi(argv[1]);
    
    printf("plaintext:");
    string plaintext=get_string();
    
    if (plaintext!=NULL)
    {
       printf("ciphertext:");
       
        //iterate over the characters in the plaintext one at a time
        for(int i=0, n=strlen(plaintext); i<n; i++)
        {
            //check if [i] character is alphabetic character and uppercase
            if (isalpha(plaintext[i])&&isupper(plaintext[i]))
            {
                //find alphabetic index of a character in plaintext
                int alph_index;
                alph_index=plaintext[i]%65;
                
                //find and print corresponding character in ciphertext in ASCII in uppercase
                int cyphertext;
                cyphertext=65+(alph_index+key)%26;
                
                printf("%c", cyphertext);
            }    
             else
             {
                //check if [i] character is alphabetic character and lowercase
                 if (isalpha(plaintext[i])&&islower(plaintext[i]))
                 {
                     //find alphabetic index of a character in plaintext
                     int alph_index;
                     alph_index=plaintext[i]%97;
                     
                     //find and print corresponding character in ciphertext in ASCII in lowercase
                     int cyphertext;
                     cyphertext=97+(alph_index+key)%26;
                     printf("%c", cyphertext);
                 }
                 else 
                 {
                     //print [i] character if it is not alphabetic character
                     printf("%c", plaintext [i]);
                 }
             
             }
        }     
    }
    }
    printf("\n");
    return 0;
}

caesar.py

# program that encrypts messages using Caesar’s cipher

def main():

    import sys
    import cs50

    #make sure a user gives a secret key from command line
    if len(sys.argv)!=2:
      print("missing command-line argument")
      exit (1)
    else:
       key = int(sys.argv[1]) #command-line argument gives a string, we use int to convert it to an integer

       print("plaintext:", end="")
       plaintext = cs50.get_string()

    if plaintext != None:
         print("ciphertext: ", end="")

         #iterate over the characters in the plaintext one at a time
         for char in plaintext:
            #check if char character is alphabetic character and uppercase
            if str.isalpha(char) and str.isupper(char):
                #find alphabetic index of a character in plaintext
                alph_index = ord(char)%65

                #find and print corresponding character in ciphertext
                cyphertext = chr((65+(alph_index+key)%26))
                print(cyphertext, end="")

            #check if char character is alphabetic character and lowercase
            elif str.isalpha(char) and str.islower(char):
                #find alphabetic index of a character in plaintext
                alph_index = ord(char)%97

                #find and print corresponding character in ciphertext
                cyphertext = chr((97+(alph_index+key)%26))
                print(cyphertext, end="")
            else:
                #print char character if it is not alphabetic character
                print(char, end="")

    print()
    exit(0)

if __name__ == "__main__":
    main()