2 files changed, 179 insertions, 1 deletions
diff --git a/ch5/5-14_rsort.c b/ch5/5-14_rsort.c
index 4928f80..4c03191 100644
--- a/ch5/5-14_rsort.c
+++ b/ch5/5-14_rsort.c
@@ -4,7 +4,7 @@
 
 /* The C Programming Language: 2nd Edition
  *
- * Exercise 5-13: Modify the sort program to handle a -r flag, which
+ * Exercise 5-14: Modify the sort program to handle a -r flag, which
  * indicates sorting in reverse (decreasing) order. Be sure that -r works
  * with -n.
  */
diff --git a/ch5/5-15_sort-fold.c b/ch5/5-15_sort-fold.c
new file mode 100644
index 0000000..1eccc34
--- /dev/null
+++ b/ch5/5-15_sort-fold.c
@@ -0,0 +1,178 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-15: Add the option -f to fold upper and lower case together, so
+ * that case distinctions are not made during sorting; for example, a and A
+ * compare equal.
+ */
+
+#define MAXLINES 5000
+char *lineptr[MAXLINES];
+
+#define MAXLEN 1000
+#define DEFAULT_LINES 10
+#define ALLOCSIZE 10000000
+
+static char allocbuf[ALLOCSIZE];
+static char *allocp = allocbuf;
+char *alloc(int);
+
+int readlines(char *lineptr[], int nlines);
+void writelines(char *lineptr[], int nlines);
+void reverse_set(char *lineptr[], int nlines);
+void my_qsort(void *lineptr[], int left, int right, int (*comp)(const char *, const char *));
+int numcmp(const char *, const char *);
+void line_tolower(char *s);
+int istrcmp(const char *, const char *);
+
+void my_qsort(void *v[], int left, int right, int (*comp)(const char *, const char *)) {
+	int i, last;
+	void swap(void *v[], int, int);
+
+	if (left >= right) {
+		return;
+	}
+	swap(v, left, (left + right) / 2);
+	last = left;
+	for (i = left + 1; i <= right; i++) {
+		if ((*comp)(v[i], v[left]) <= 0) {
+			swap(v, ++last, i);
+		}
+	}
+	swap(v, left, last);
+	my_qsort(v, left, last - 1, comp);
+	my_qsort(v, last + 1, right, comp);
+}
+
+int numcmp(const char *s1, const char *s2) {
+	double v1, v2;
+
+	v1 = atof(s1);
+	v2 = atof(s2);
+	if (v1 < v2) {
+		return -1;
+	} else if (v1 > v2) {
+		return 1;
+	} else {
+		return 0;
+	}
+}
+
+void swap(void *v[], int i, int j) {
+	void *temp;
+
+	temp = v[i];
+	v[i] = v[j];
+	v[j] = temp;
+}
+
+int readlines(char *lineptr[], int maxlines) {
+	int len, nlines;
+	char *p, line[MAXLEN];
+	nlines = 0;
+	while ((len = mygetline(line, MAXLEN)) > 0) {
+		if (nlines >= maxlines || (p = alloc(len)) == NULL) {
+			return -1;
+		} else {
+			line[len-1] = '\0';
+			strcpy(p, line);
+			lineptr[nlines++] = p;
+		}
+	}
+	return nlines;
+}
+
+void writelines(char *lineptr[], int nlines) {
+	int i = 0;
+	for (; i < nlines && lineptr[i] != NULL; i++) {
+		printf("%s\n", lineptr[i]);
+	}
+}
+
+void reverse_set(char *lineptr[], int nlines) {
+	int i;
+	int j = nlines;
+	for (i = 0; i < (nlines / 2); i++, j--) {
+		if (i < nlines) {
+			swap((void **)lineptr, i, j);
+		}
+	}
+}
+
+/* Lowercase the entire line */
+void line_tolower(char *s) {
+	int i;
+	for (i = 0; s[i] != '\0'; i++) {
+		s[i] = tolower(s[i]);
+	}
+}
+
+/* Ignore character case, then send results to qsort */
+int istrcmp(const char *s1, const char *s2) {
+	for ( ; tolower(*s1) == tolower(*s2); s1++, s2++) {
+		if (*s1 == '\0') {
+			return 0;
+		}
+	}
+	return tolower(*s1) - tolower(*s2);
+}
+
+int mygetline(char *line, int lim) {
+	int c, i;
+	for (i = 0; i < lim && (c = getchar()) != EOF && c != '\n'; i++) {
+		*(line++) = c;
+	}
+	if (c == '\n') {
+		i++; /* I count newlines; some don't */
+		*(line++) = c;
+	}
+	*line = '\0';
+	return i;
+}
+
+char *alloc(int n) {
+	if (allocbuf + ALLOCSIZE - allocp >= n) {
+		allocp += n;
+		return allocp - n;
+	} else {
+		return 0;
+	}
+}
+
+/* sort input lines */
+int main (int argc, char *argv[]) {
+	int nlines;        /* number of input lines read */
+	int numeric = 0;   /* 1 if numeric sort */
+	int reverse = 0;   /* 1 if reverse sort */
+	int fold = 0;      /* 1 if folding upper and lower case */
+
+	if (argc > 1) {
+		int i;
+		for (i = 1; --argc; i++) {
+			if (strcmp(argv[i], "-n") == 0) {
+				numeric = 1;
+			} else if (strcmp(argv[i], "-r") == 0) {
+				reverse = 1;
+			} else if (strcmp(argv[i], "-f") == 0) {
+				fold = 1;
+			}
+		}
+	}
+	if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
+		/* The trick is to chain inline if-statements. This will point to the correct
+		function for comparison, which powers my_qsort */
+		my_qsort((void **) lineptr, 0, nlines - 1, (int (*)(const char *, const char *))(numeric ? numcmp : (fold ? istrcmp : strcmp)));
+		if (reverse == 1) {
+			reverse_set(lineptr, nlines - 1);
+		}
+		writelines(lineptr, nlines);
+		return 0;
+	} else {
+		printf("Input too big to sort\n");
+		return 1;
+	}
+}