Programming

#include <stdio.h>
#include <ctype.h>
#include <errno.h>

int main(int argc, char *argv[])
{
    int c, hx;

    hx = 0;
    while ((c = getchar()) != EOF && c != '\n') {
        if (isdigit(c))
            hx = c - '0' + hx * 10;
        else {
            perror(argv[0]);
            return 1;
        }
    }
    printf("%x\n", hx);
    return 0;
}

#include <stdio.h>

int main(int argc, char *argv[])
{
    int c, hx;
    if (argc > 1)
    {
         hx=atol(argv[1]);
    }
    else
    {
         scanf("%d",&hx);
    }
    printf("%x\n", hx);
    return 0;
}