Command-line validation key

Question

I cannot figure out why am I getting these results?

I'm currently only trying to validate the Numeric Key when typing 20x as a command-line argument get Usage: ./caesar Key

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

int main (int argc, string argv[])
{
    int Key = (int)argv[1];

    if (argc == 2)
    {
       for (int i = 0, n = strlen(argv[1]); i < n; i++)
       {
           if (argv[1][i] >= 48 && argv[1][i] <= 57)
           {
               printf("Success\n");
               printf("%s\n", argv[1]);
           }
           else
           {
               printf("Usage: ./caesar Key\n"); 
               return 1;
           }
       }

    }
    else 
    {
        printf("Usage: ./caesar Key\n");
    }
}

Answer 1

Maybe it's because you're trying to cast 20x into a integer, try doing these conditions, if argc != 2 then end the program, if argv[1] has a non numeric character then end the program. The arguments that your program should take should only be integers.