Exercise 5.01

Page 97

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.

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

#define SIZE 100

int main()
{
	int n, isnum, array[SIZE], getint(int *);

	for (n = 0; n < SIZE && (isnum = getint(&array[n])) != EOF;
	     isnum ? n++ : (void)0)
		;

	for (int i = 0; i < n; i++) {
		printf("%d\n", array[i]);
	}
}

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

int getint(int *pn)
{
	int c, sign;

	while (isspace(c = getch()))
		;

	if (!isdigit(c) && c != EOF && c != '+' && c != '-') {
		return 0;
	}

	sign = (c == '-') ? -1 : 1;

	if (c == '+' || c == '-') {
		c = getch();
		if (c <= '0' || c >= '9') {
			return 0;
		}
	}

	for (*pn = 0; isdigit(c); c = getch()) {
		*pn = 10 * *pn + (c - '0');
	}

	*pn *= sign;

	if (c != EOF) {
		ungetch(c);
	}

	return c;
}

#define BUFSIZE 100
char buf[BUFSIZE];
int bufp = 0;

int getch(void)
{
	return (bufp > 0) ? buf[--bufp] : getchar();
}

void ungetch(int c)
{
	if (bufp >= BUFSIZE) {
		printf("ungetch: too many characters\n");
	} else {
		buf[bufp++] = c;
	}
}