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-rw-r--r--ch5/5-06_pointer-funcs.c154
1 files changed, 154 insertions, 0 deletions
diff --git a/ch5/5-06_pointer-funcs.c b/ch5/5-06_pointer-funcs.c
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+++ b/ch5/5-06_pointer-funcs.c
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+#include <stdio.h>
+#include <ctype.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-6: Rewrite appropriate programs from earlier chapters and
+ * exercises with pointers instead of array indexing. Good possibilites
+ * include getline (Chapters 1 and 4), atoi, itoa, and their variants
+ * (Chapters 2, 3, and 4), reverse (Chapter 3), and strindex and getop
+ * (Chapter 4).
+ *
+ * Answer: This is more of the same. Practice or homework, basically. Thing is,
+ * I hate homework, so let's do the bare minimum and only do the functions
+ * that were explicitly listed. :)
+ *
+ * A cool side effect of using pointers is pointer-based functions seem to be
+ * shorter!
+ */
+
+int get_line(char *, int);
+int atoi(char *);
+void itoa(int, char *);
+void reverse(char *);
+int strindex(char *, char *);
+int getop(char *);
+
+int main() {
+ // simplistic testing, nothing fancy, screw busywork
+ char foo[20] = "foobar";
+ char bar[50];
+ int baz;
+ reverse(foo);
+ printf("Let's test reverse(\"foobar\"): %s\n", foo);
+ printf("Enter some text to test get_line(): ");
+ if ((baz = get_line(bar, 50)) > 0) {
+ printf("get_line() returns %d and updates to: %s", baz, bar);
+ }
+ printf("atoi(): %d\n", atoi("7529"));
+ itoa(-4321, bar);
+ printf("itoa(): %s\n", bar);
+ printf("strindex(\"foobarness\", \"bar\"): %d\n", strindex("foobarness", "bar"));
+ printf("Enter a RPN equation to test getop(): ");
+ printf("getop(): %d, %s\n", getop(bar), bar);
+ return 0;
+}
+
+void reverse(char *s) {
+ char *end = s;
+ char tween;
+ while (*end != '\0') {
+ end++;
+ }
+ end--; // get behind the \0
+ while (end > s) {
+ tween = *end;
+ *end-- = *s;
+ *s++ = tween;
+ }
+}
+
+int get_line(char *s, int lim) {
+ int c, i;
+ for (i = 0; i < lim - 1 && (c=getchar()) != EOF && c != '\n'; ++i) {
+ *s++ = c;
+ }
+ if (c == '\n') {
+ *s++ = c;
+ i++;
+ }
+ *s = '\0';
+ return i;
+}
+
+int atoi(char *s) {
+ int n, sign;
+ while (isspace(*s)) {
+ s++;
+ }
+ sign = (*s == '-') ? -1 : 1;
+ if (*s == '+' || *s == '-') {
+ s++;
+ }
+ for (n = 0; isdigit(*s); n = 10 * n + (*s - '0'), s++);
+ return n * sign;
+}
+
+void itoa(int n, char *s) {
+ char *start = s;
+ int sign = 0;
+ if (n < 0) {
+ sign = 1;
+ n = -n;
+ }
+ do {
+ *s = '0' + (n % 10);
+ s++;
+ } while ((n /= 10) > 0);
+ if (sign) {
+ *s = '-';
+ s++;
+ }
+ *s = '\0';
+ reverse(start);
+}
+
+int strindex(char *s, char *t) {
+ int loc;
+ int len;
+ for (loc = 0; *s != '\0'; loc++, s++) {
+ for (len = 0; *t != '\0' && *s == *t; len++, s++, t++);
+ if (len > 0 && *t == '\0') {
+ return loc;
+ }
+ }
+ return -1;
+}
+
+/* This function is useless on its own. It should be used in a calculator
+ * application that has an input buffer. Regardless, it should still store the
+ * operand in a string and return an integer; that's all testable.
+ */
+int getop(char *s) {
+ int c, next;
+ while ((c = *s = getchar()) == ' ' || c == '\t');
+ s++;
+ *s = '\0';
+ if (!isdigit(c) && c != '.' && c != '-') {
+ return c;
+ }
+ if (c == '-') {
+ next = getchar();
+ if (!isdigit(next) && next != '.') {
+ return c;
+ } else {
+ c = next;
+ }
+ } else {
+ c = getchar();
+ }
+ while (isdigit(*s = c)) {
+ s++;
+ c = getchar();
+ }
+ if (c == '.') {
+ *s = c;
+ s++;
+ while (isdigit(*s = c = getchar())) {
+ s++;
+ }
+ }
+ s++;
+ *s = '\0';
+ return 1; // number found
+}