Exercise 5-1: getint and a sign on its own

As written, getint treats a + or - not followed by a digit as a valid representation of zero. Fix it to push such a character back on the input.

/* getint:  get next integer from input into *pn */
int getint(int *pn)
{
    int c, sign;

    while (isspace(c = getch()))   /* skip white space */
        ;
    if (!isdigit(c) && c != EOF && c != '+' && c != '-') {
        ungetch(c);  /* it is not a number */
        return 0;
    }
    sign = (c == '-') ? -1 : 1;
    if (c == '+' || c == '-')
        c = getch();
    for (*pn = 0; isdigit(c); c = getch())
        *pn = 10 * *pn + (c - '0');
    *pn *= sign;
    if (c != EOF)
        ungetch(c);
    return c;
}

Use it in a program that prints each integer in its input on a line of its own, including one right at the end of the input, and skips any character that doesn't start an integer.