vigenere.c

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

int main(int argc, string argv[])
{
    // ensure that user input a key
    if (argc > 1 && argc < 3)
    {
        int s = strlen(argv[1]);
        // create array for string
        int key[s];
        // get plaintext string from user
        string m = GetString();
        // do for the length of plaintext string
        for (int j = 0, i = 0, num = strlen(m); j <= num; j++, i++)
        {
            // check case and validitiy of char in array
            if (islower(argv[1][j]))
            {
                // assign jth char of key to jth char of argv
                key[j] = (argv[1][j] - 97);
                // check message case for ith char
                if((m[i] >= 'A') && (m[i] <= 'Z'))
                {
                    m[i] = ((m[i] -'A') + key[j % strlen(argv[1])]) % 26 +'A';
                    printf("%c", m[i]);
                }

                if((m[i] >= 'a') && (m[i] <= 'z'))
                {
                    m[i] = ((m[i] -'a') + key[j % strlen(argv[1])]) % 26 +'a';
                    printf("%c", m[i]);
                }
            }
            else if (isupper(argv[1][j]))
            {
                key[j] = (argv[1][j] - 65);
                if((m[i] >= 'A') && (m[i] <= 'Z'))
                {
                    m[i] = ((m[i] -'A') + key[j % strlen(argv[1])]) % 26 +'A';
                    printf("%c", m[i]);
                }

                if((m[i] >= 'a') && (m[i] <= 'z'))
                {
                    m[i] = ((m[i] -'a') + key[j % strlen(argv[1])]) % 26 +'a';
                    printf("%c", m[i]);
                }

            }
        }
        printf("\n");
        return 0;

     }
     else
        printf("You must enter a key!\n");
        return 1;
}