C语言，求问这个oj怎么写？

#include<stdio.h>

int main()
{
    char ch;
    scanf("%c",&ch);
    if(ch-'0'>=0&&ch-'0'<=9) printf("Yes,it is a digit.\n");
    else printf("No,it is not a digit.\n");
    return 0;
}

int main()
{
    char ch;
    scanf("%c", &ch);
    printf("%s",
            ( is_digit(ch) ? "Yes, it is a digit."
                          : "No, it is not a digit." )
          );
    return 0;
}