Exercise 4.8 - getch and ungetch handling pushback character¶

/**
 * Suppose that there will never be more than one character
 * for pushback. Modify getch and ungetch accordingly.
 **/

#include <stdio.h>

char buf = 0;

/* getch: get a (possibly) pushed back character */
int getch(void)
{
	int c;

	if(buf != 0)
		c = buf;
	else
		c = getchar();

	buf = 0;
	return c;
}

/* ungetch: push a character back into input */
void ungetch(int c)
{
	if(buf != 0)
		printf("ungetch: too many characters\n");
	else
		buf = c;
}

int main(void)
{
	int c;

	c = '*';

	ungetch(c);

	while((c=getch()) != EOF)
		putchar(c);

	return 0;
}