CS50

caesar.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 1 Key\n");
        return 1;
    }
    int key = atoi (argv[1]);
    string s = GetString();
    if (s != NULL) {
        for (int i = 0, length = strlen(s); i < length; i++) {
            if (isalpha(s[i])) {
                if (isupper(s[i])) {
                    s[i] -= 65;
                    s[i] = (s[i] + key) % 26;
                    s[i] += 65;
                }
                else {
                    s[i] -= 97;
                    s[i] = (s[i] + key) % 26;
                    s[i] += 97;
                }
            }
            printf ("%c", s[i]);
        }
        printf ("\n");
    }
}