A C Miscellany

　　1. ungetch () to return a character into the keyboard buffer

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

int getch(void);
void ungetch(int);

int getint(int *pn)
{
    int c, sign;
    while (isspace(c = getch()))
    ;
    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 = getchar())
        *pn = 10 * *pn +(c - '0');
    *pn *= sign;
    if (c != EOF)
     ungetch(c);
    return c;
}

　　2. The address of the first element of the array array delegates

　　3 by a pointer can be achieved through the array and an offset index and expression achieved, it should be noted that the pointer is a variable, rather than a variable array name