From 19fa3daff1447c633029e1730bf0355b21ee029f Mon Sep 17 00:00:00 2001
From: zlg <zlg@zlg.space>
Date: Mon, 26 Nov 2012 20:45:37 -0600
Subject: Solve Exercise 1-21: entab

---
 1-20_detab.c | 16 +++++++++++-----
 1-21_entab.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 5 deletions(-)
 create mode 100644 1-21_entab.c

diff --git a/1-20_detab.c b/1-20_detab.c
index 3101610..e1549e6 100644
--- a/1-20_detab.c
+++ b/1-20_detab.c
@@ -5,11 +5,15 @@
  * "Write a program `detab` that replaces tabs in the input with the proper
  * number of blanks to space to the next tabstop. Assume a fixed set of
  * tabstops, say every 'n' columns. Should 'n' be a variable or a symbolic
- * parameter?
+ * parameter?"
  *
  * Answer: 'n' should be a symbolic parameter. It's more apparent what's being
  * worked with and it's not susceptible to scope. Though, in this simple
  * program it really doesn't matter.
+ *
+ * To be correct, this file should use the isprint() function to ensure that
+ * 'column' only gets incremented when a printable character is being read. I'll
+ * come back to this when I learn more of the stdlib.
  */
 
 #define TABWIDTH 8
@@ -30,12 +34,14 @@ int main(void) {
 				++column;
 			}
 		} else {
-			// non-tabs simply get output.
-			putchar(c);
-			++column;
-			// Line-endings should reset the column counter after being output.
 			if (c == '\n') {
+				// Line-endings should reset the column counter after being output.
+				putchar(c);
 				column = 0;
+			} else {
+				// Now we can just output and increase column!
+				putchar(c);
+				++column;
 			}
 		}
 	}
diff --git a/1-21_entab.c b/1-21_entab.c
new file mode 100644
index 0000000..595f583
--- /dev/null
+++ b/1-21_entab.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+
+/* The C Programming Language: 2nd Edition
+ * Exercise 1-21:
+ * "Write a program `entab` that replaces strings of blanks by the minimum
+ * number of tabs and blanks to achieve the same spacing. Use the same tab
+ * stops as for `detab`. When either a tab or a single blank would suffice to
+ * reach a tab stop, which should be given preference?"
+ *
+ * Answer: A blank. A tab character that comes after (tabstop - 1) blanks makes
+ * little-to-no sense and could mess up alignment in some environments.
+ *
+ */
+
+#define TABWIDTH 8
+
+int main(void) {
+	int c, spaces;
+	spaces = 0;
+	while ((c = getchar()) != EOF) {
+		// Make sure the character is a space...
+		if (c == ' ') {
+			++spaces;
+			// When spaces is equal to TABWIDTH, we can add a tab
+			if (spaces == TABWIDTH) {
+				putchar('\t');
+				spaces = 0;
+			}
+		} else {
+			/* As soon as we hit a non-space character, we need to make sure
+			 * there aren't 1-7 spaces leftover. These need to be output before
+			 * we output the non-space character itself! This little loop is
+			 * interesting because it solves the problem of leftover spaces
+			 * _and_ gets the 'spaces' back to zero, which it needs to be once
+			 * we hit a non-space character.
+			 */
+			while (spaces != 0) {
+				putchar(' ');
+				--spaces;
+			}
+			// Output the non-space character.
+			putchar(c);
+		}
+	}
+}
-- 
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