CS50

vigenere.c

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

int main (int argc, string argv[]) {
    if (argc != 2) {
        printf ("Please Enter Exactly 1 Key\n");
        return 1;
    }
    string key = argv[1];
    int lengthk = strlen(key);
    for (int i = 0; i < lengthk; i++) {
        if (isalpha(key[i])) {
            if (isupper(key[i])) 
                key[i] -= 65;
            else
                key[i] -= 97;
        }
        else {
            printf ("Please Enter a Text Key\n");
            return 1;
        }
    }
    string s = GetString();
    int lengths = strlen(s);
    int j = 0;
    for (int i = 0; i < lengths; i++) {
        j %= lengthk;
        if (isalpha(s[i])) {
            if (isupper(s[i])) {
                s[i] -= 65;
                s[i] = (s[i] + key[j]) % 26;
                s[i] += 65;
            }
            else {
                s[i] -= 97;
                s[i] = (s[i] + key[j]) % 26;
                s[i] += 97;
            }
            j++;
        }
        printf ("%c", s[i]);
    }
    printf ("\n");
}