Solve Exercise 5-1: fixed getint()

2 files changed, 82 insertions, 13 deletions

diff --git a/README.mdown b/README.mdown
index f5d961a..4b12335 100644
--- a/README.mdown
+++ b/README.mdown
@@ -1,16 +1,20 @@
 These files are my solutions to Kernighan and Ritchie's *The C Programming
-Language, 2nd Edition*. My aim is to deepen my understanding of C, using only
-the concepts covered in content that comes before each exercise. That means no
-"cheating" by using standard library features that aren't covered in the book
-yet. As a result, many of my solutions will probably not be "the best", but
-suitable for the goal at hand: *learning*.
+Language, 2nd Edition*. The aim is to deepen my understanding of C, using only
+the concepts covered in content that comes before each exercise. That means
+no "cheating" by using standard library features that aren't covered in the
+book yet. According to [`comp.lang.c`][clc], this is known as *Category-0
+compliant*. As a result, many of my solutions will probably not be "the best",
+but suitable for the goal at hand: *learning*.
 
-I chose this route because as I was reading the K&R, I didn't feel like I was 
-learning anything new, but I knew C was known for its simplicity and efficiency. 
-If I wasn't learning anything about efficiency and simplifying my programs, then 
-why was I learning C? I tackled a few exercises and found that I was beginning 
-to learn a few things I hadn't ran into before.
+I chose this route because as I read through the K&R, I didn't feel like I
+was learning anything new. C is known for its simplicity and efficiency, so
+I thought, "If I'm not learning anything about efficiency and simplifying
+my programs, then why am I learning C?" I tackled a few exercises and found
+that I was beginning to learn a few things I hadn't ran into before, and this
+repository was born.
 
-Critique is welcome, but please keep in mind the limitations I've outlined in 
-the first paragraph. Also note that some incomplete implementations are noted,
-which I intend on revisiting. Any suggestions and advice are welcome.
+Critique is welcome, but please keep in mind the limitations I've outlined in
+the first paragraph. Some incomplete implementations are noted, which I intend
+on revisiting or annotating. Any questions, suggestions, and advice are welcome.
+
+[clc]: http://clc-wiki.net/wiki/K%26R2_solutions:Ancillary:Category_numbers
diff --git a/ch5/5-01_getint-fixed.c b/ch5/5-01_getint-fixed.c
new file mode 100644
index 0000000..8d53ba6
--- /dev/null
+++ b/ch5/5-01_getint-fixed.c
@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <ctype.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-1: 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.
+ */
+
+#define BUFSIZE 100
+
+int getch(void);
+void ungetch(int);
+int getint(int *);
+
+char buf[BUFSIZE];
+int bufp = 0;
+
+int main() {
+	int foo;
+	int *bar = &foo;
+	while (getint(bar) > 0) {
+		printf("%d\n", foo);
+	}
+	return 0;
+}
+
+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();
+	}
+	if (!isdigit(c)) {
+		return 0;
+	}
+	for (*pn = 0; isdigit(c); c = getch()) {
+		*pn = 10 * *pn + (c - '0');
+	}
+	*pn *= sign;
+	if (c != EOF) {
+		ungetch(c);
+	}
+	return c;
+}
+
+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;
+	}
+}