Exercise 5.1. As written, getint treats a + or - not followed by a digit as a valid representation of zero.

Exercise 5.1. 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, mark;

    

    while(isspace(c = getch())) //skip white space

        ;

    if(!isdigit(c) && c != EOF && c != '+' && c != '-')

    {

        ungetch(c); //it's not a number

        return 0;

    }

    sign = (c == '-') ? -1 : 1;

    if(c == '+' || c == '-')

    {

        mark = c; //remember a sign

        c = getch();

        if(!isdigit(c))

        {

            if(c != EOF)

                ungetch(c); //not a number - back on the input

            ungetch(mark); //back sign of the symvol on the input

            return 0; 

        }

    }

    for(*pn = 0; isdigit(c); c = getch())

        *pn = 10 * *pn + (c - '0');

    *pn *= sign;

    if(c != EOF)

        ungetch(c);

    return c;

}