CaesarNotDone

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


int main(int argc, string argv[])
{
    int j = 0, f = 0, n = strlen(argv[1]);

    if(argc == 2)
    {
        for (int i = 0; i < n; i++)
        {
            if(isalpha(argv[1][i]) == 0 && isdigit(argv[1][i]))
            {
                j++;
            }
        }
    }
    else if (argc != 2)
    {
        printf("Usage:./caesar key \n");
        return 1;
    }

    if(j == n)
    {
        string plainText = get_string("Enter text you wish to encode: ");
        int b = strlen(plainText);
        printf("plaintext: %s\n", plainText);

        for (int i = 0; i < b; i++)
        {
            f = atoi(argv[1]);
            if(isalpha(plainText[i]) && isupper(plainText[i]))
            {
                plainText[i] = plainText[i] - 65;
                plainText[i] = (plainText[i] + f) % 26;
                plainText[i] = plainText[i] + 65;
            }
            else if (isalpha(plainText[i]) && islower(plainText[i]))
            {
                plainText[i] = plainText[i] - 97;
                plainText[i] = (plainText[i] + f) % 26;
                plainText[i] = plainText[i] + 97;
            }
        }

        printf("ciphertext: ");
        for (int i = 0; i < b; i++)
        {
            printf("%c", plainText[i]);
        }
        printf("\n");
    }
    else
    {
        printf("Usage:./caesar key \n");
        return 1;
    }
}