Solve Exercise 5-11: `entab` and `detab` remixed!

This one was pretty rough. At first I wanted to include a bunch of
error-catching and "smart" stuff. When I took a second look at it and
realized `itoa` returns 0 on a string, things became a bit easier. I
may have been able to outsource a few things to a function or two, but
overall I think it worked out.

2 files changed, 137 insertions, 0 deletions

diff --git a/ch5/5-11_detab-remixed.c b/ch5/5-11_detab-remixed.c
new file mode 100644
index 0000000..43bffb4
--- /dev/null
+++ b/ch5/5-11_detab-remixed.c
@@ -0,0 +1,61 @@
+#include <stdio.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-11: Modify the programs entab and detab (written as exercises in
+ * Chapter 1) to accept a list of tab stops as arguments. Use the default tab
+ * settings if there are no arguments.
+ */
+
+#define TABWIDTH 8
+
+int main(int argc, char *argv[]) {
+	int column, c, tabnum, stop;
+	column = 0;
+
+	if (argc > 1) {
+		tabnum = 1;
+		stop = atoi(argv[tabnum]);
+	} else {
+		tabnum = 0;
+	}
+
+	while ((c = getchar()) != EOF) {
+		if (c == '\t') {
+			if (argc > 1) {
+				// advance the argument if we're ahead of the last one
+				if (column > stop && tabnum < (argc -1)) {
+					stop = atoi(argv[++tabnum]);
+				}
+				// insert our spaces up to the tabstop
+				while (column <= stop) {
+					putchar(' ');
+					column++;
+				}
+				// advance the argument (again) if needed.
+				if (tabnum < (argc - 1)) {
+					stop = atoi(argv[++tabnum]);
+				}
+			} else {
+				// default tabstopping
+				while (column % TABWIDTH != 1) {
+					putchar(' ');
+					column++;
+				}
+			}
+		} else {
+			// reset counters and the arglist
+			if (c == '\n') {
+				column = 0;
+				if (tabnum > 0) {
+					tabnum = 1;
+					stop = atoi(argv[tabnum]);
+				}
+			}
+			putchar(c);
+			column++;
+		}
+	}
+
+	return 0;
+}
diff --git a/ch5/5-11_entab-remixed.c b/ch5/5-11_entab-remixed.c
new file mode 100644
index 0000000..8f6f7d4
--- /dev/null
+++ b/ch5/5-11_entab-remixed.c
@@ -0,0 +1,76 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-11: Modify the programs entab and detab (written as exercises in
+ * Chapter 1) to accept a list of tab stops as arguments. Use the default tab
+ * settings if there are no arguments.
+ */
+
+/* The directions for this exercise aren't terribly clear. The way I see it,
+ * each argument is a character column that all tabs should align to. For the
+ * entab portion, I should count 2+ spaces forward and, if I reach a tabstop,
+ * insert a tab. Then move onto the next argument. If 2+ spaces are present,
+ * but don't reach the tabstop threshold, the spaces are left alone. This is
+ * the best I could manage with the ambiguous instructions.
+ */
+
+#define TABWIDTH 8
+
+int main(int argc, char *argv[]) {
+	int column, c, spaces, tabnum, stop;
+	spaces = column = 0;
+
+	if (argc > 1) {
+		tabnum = 1;
+		stop = atoi(argv[tabnum]);
+	} else {
+		tabnum = 0;
+	}
+
+	while ((c = getchar()) != EOF) {
+		column++;
+
+		if (c == ' ') {
+			spaces++;
+			if (argc > 1) {
+				if (column == stop) {
+					if (tabnum < (argc - 1)) {
+						stop = atoi(argv[++tabnum]);
+					}
+					if (spaces > 1) {
+						putchar('\t');
+						spaces = 0;
+					}
+				} else if (column > stop && tabnum < (argc -1)) {
+					stop = atoi(argv[++tabnum]);
+				}
+			} else {
+			// we need to do default tabstopping
+				if (column % TABWIDTH == 0 && spaces > 1) {
+					putchar('\t');
+					spaces = 0;
+				}
+			}
+		} else {
+			// output all extra spaces first
+			while (spaces > 0) {
+				putchar(' ');
+				spaces--;
+			}
+			// reset the counts and argument position on a newline
+			if (c == '\n') {
+				column = 0;
+				spaces = 0;
+				if (tabnum > 0) {
+					tabnum = 1;
+					stop = atoi(argv[tabnum]);
+				}
+			}
+			putchar(c);
+		}
+	}
+	
+	return 0;
+}