vigenere

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

int shift(char c);

int main(int argc, string argv[])

{
    if (argc != 2) //if user doesn't run command-line argument of one or enter positive int
    {
        printf("Usage: ./vigenere key\n"); //prompt them to run it again
        return 1; //returning zero means everything went well
    }

    for (int j = 0, n = strlen(argv[1]); j < n; j++)  //length of the entire string. Save n as strlen for use in loop
    {
        if (isalpha(argv[1][j])) //if user doesn't run command-line argument of one or enter positive int and user inputs an alpha key, continue

        {
            //printf("%c\n", argv[1][j]); //Print after collecting plaintext
        }


        else

        {
            printf("Usage: ./vigenere key\n"); //prompt them to run it again
            return 1; //returning zero means everything went well
        }

    }

    printf("ciphertext: ");

    string p = get_string("plaintext: "); //prompt for plaintext and store
    string key = argv[1]; //declare the key as a string
    char cipher; //declare cipher as a char

    //NOW ROTATE BY THE KEY

    for (int i = 0; j = 0; i < strlen(p); i ++) //length of the entire string

    {
        if (j == strlen(key)) //if j reaches the end of the string, start over

            {
                j = 0;
            }

        if (isupper(p[i]))

        {
            cipher = (((p[i] + shift(key[j])) - 65) % 26) + 65; //Use the new shift function now
            printf("%c", cipher); //print ciphertext after rotating
            j++;
        }

        else if (islower(p[i]))

        {
            cipher = (((p[i] + shift(key[j])) - 97) % 26) + 97; //add key and rotate
            printf("%c", cipher); //print ciphertext after rotating
            j++;
        }

        else

        {
            printf("%c", p[i]);
        }

    }

    printf("\n");
    return 0;


} //Closing braces



//function definition
int shift(char c); //NEW SHIFT function
{
    int k;

    if (islower(c))
        {
            k = c - 97;
        }

    if (isupper(c))
        {
            k = c - 65;
        }

    return k;

}