getint: pointer version.

#include <ctype.h>
int getch(void);
void ungetch(int);

/* 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);
        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;
}