check digit

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

int main(int argc, string argv[])
{    
    // Check if 2 commandline arguments are given, otherwise abort program
    if (argc == 2)
    {
        // Determine length of argv[1] to use as upper limit for for loop
        int n = strlen(argv[1]);
        // Loop through argv[1] to check if only numeric inputs are given, else abort program
        for (int i = 0; i < n; i++)
        {
            if (isdigit(argv[1][i]))
            {
                printf ("%c\n", argv[1][i]);
                printf ("Success\n");
            }
            else 
            {
                printf ("Usage: ./ceasar key\n");
                return 1;
            }
        }
    }
    else
    {
        printf ("Usage: ./ceasar key\n");
        return 1;
    };
    
    // Transform argv[1] to int and assign to key variable
    int key = atoi(argv[1]);
    printf ("%i\n", key);
}