1 /*
2  * Exercise 4-9. Our getch and ungetch do not handle a pushed-back EOF
3  * correctly. Decide what their properties ought to be if an EOF is pushed
4  * back, then implement your design.
5  *
6  * EOF is defined as -1, so we need to change the buffer from an array of
7  * chars to an array of ints. The functions are otherwise identical
8  */
9 
10 #include <stdio.h>
11 #include <string.h>
12 
13 #define MAXLEN 1000 /* max size of buffer */
14 
15 int getch(void);
16 void ungetch(int);
17 void ungets(char []);
18 
19 int main() {
20 	char s[MAXLEN];
21 	int i = 0;
22 	char c;
23 	while ((s[i++] = c = getch()) != EOF) {
24 		if (c == '*') {
25 			ungets("test"); 
26 			i--;
27 		}
28 	}
29 	s[i] = '\0';
30 	printf("%s\n", s);
31 }
32 
33 #define BUFSIZE 100
34 
35 int buf[BUFSIZE]; /* buffer for ungetch */
36 int bufp = 0;
37 
38 /* get a (possibly pushed back) character */
39 int getch(void) {
40 	return (bufp > 0) ? buf[--bufp] : getchar();
41 }
42 
43 /* push character back on input */
44 void ungetch(int c) {
45 	if (bufp >= BUFSIZE)
46 		printf("ungetch: too many characters\n");
47 	else
48 		buf[bufp++] = c;
49 }
50 
51 void ungets(char s[]) {
52 	int i = strlen(s);
53 	while (i > 0)
54 		ungetch(s[--i]);
55 }