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

int main(int argc, string argv[])
{
    while (argc!=2){
        printf("Usage: ./caesar key\n");
        return 1;
    }
    for (int w = 0; w<strlen(argv[1]); w++){
         char d = argv[1][w];
         if(d<48 || d>57)
         {
             printf("Usage: ./caesar key\n");
             return 1;
         }
    }
    int k = atoi(argv[1]);

    string a = get_string("plaintext: ");
    printf("ciphertext: ");
    for (int i = 0, n = strlen(a); i < n; i++)
    {
        char p = a[i];

        if (a[i] >= 'a' && a[i] <= 'z')
        {
            char c = p + k;
            if (c > 'z')
            {
                c=(c-'z')+('a'-1);
            }
            printf("%c", c);
        }
       else if (a[i] >= 'A' && a[i] <= 'Z')
        {
            char c = p + k;
            if (c > 'Z')
            {
                c=(c-'Z')+('A'-1);
            }
            printf("%c", c);
        }
        else {
            printf("%c", a[i]);
        }
    }
}