From 920346f5b7373fd806511c61ea8c20d8306e5cb7 Mon Sep 17 00:00:00 2001
From: zlg <zlg@zlg.space>
Date: Wed, 19 Jun 2013 23:44:09 -0500
Subject: Solve Exercise 4-5: adding sin(), exp(), pow()
---
ch4/4-05_math-funcs.c | 216 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 216 insertions(+)
create mode 100644 ch4/4-05_math-funcs.c
diff --git a/ch4/4-05_math-funcs.c b/ch4/4-05_math-funcs.c
new file mode 100644
index 0000000..6c22767
--- /dev/null
+++ b/ch4/4-05_math-funcs.c
@@ -0,0 +1,216 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <math.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 4-5: Add access to library functions like `sin`, `exp`, and
+ * `pow`. See <math.h> in Appendix B, Section 4.
+ *
+ * Answer: Doing this is much like 4-4; we're gonna use more special
+ * characters, and tie them to math.h functions.
+ *
+ * Note that math.h may be a separate library on your system. If you use
+ * GNU/Linux, the library may be called `libm` and can be linked to using
+ * the `-lm` gcc option when you compile. I'll remove this note when I
+ * learn how to write makefiles or something similar.
+ */
+
+#define MAXOP 100
+#define NUMBER '0'
+#define MAXVAL 100
+#define BUFSIZE 100
+
+int getop(char []);
+void push(double);
+double pop(void);
+int getch(void);
+void ungetch(int);
+void stack_top(void);
+double dupe_top(void);
+void swap_top_two(void);
+void clear_stack(void);
+
+int sp = 0; // Next free stack position
+double val[MAXVAL]; // Value stack
+char buf[BUFSIZE]; // buffer for ungetch
+int bufp = 0; // next free position in buf
+
+/* Reverse Polish calculator:
+ *
+ * Binary operations (+-*\%)
+ * operand operand operator
+ *
+ * Example: 6 minus 2 in Reverse Polish Notation is "6 2 -"
+ */
+int main() {
+ int type;
+ double op2;
+ char s[MAXOP];
+
+ while ((type = getop(s)) != EOF) {
+ switch (type) {
+ case NUMBER:
+ push(atof(s));
+ break;
+ case '+':
+ push(pop() + pop());
+ break;
+ case '*':
+ push(pop() * pop());
+ break;
+ case '-':
+ op2 = pop();
+ push(pop() - op2);
+ break;
+ case '/':
+ op2 = pop();
+ if (op2 != 0.0) {
+ push(pop() / op2);
+ } else {
+ printf("Error: Cannot divide by zero.\n");
+ }
+ break;
+ /* Yay for modulus! */
+ case '%':
+ op2 = pop();
+ if (op2 != 0.0) {
+ push((int)pop() % (int)op2);
+ } else {
+ printf("Error: Cannot modulo by zero.\n");
+ }
+ break;
+ /* Top of stack */
+ case '?':
+ stack_top();
+ break;
+ /* Dupe the top of the stack */
+ case '#':
+ dupe_top();
+ break;
+ /* Swap the top two */
+ case '~':
+ swap_top_two();
+ break;
+ /* Clear the stack */
+ case '!':
+ clear_stack();
+ break;
+ /* sin() support */
+ case '(':
+ op2 = sin(pop());
+ push(op2);
+ break;
+ /* exp() support */
+ case '{':
+ op2 = exp(pop());
+ push(op2);
+ break;
+ /* pow() support */
+ case '^':
+ op2 = pop();
+ push(pow(pop(), op2));
+ break;
+ case '\n':
+ printf("\t%.8g\n", pop());
+ break;
+ default:
+ printf("Error: Unknown command %s\n", s);
+ break;
+ }
+ }
+ return 0;
+}
+
+void push(double f) {
+ if (sp < MAXVAL) {
+ val[sp++] = f;
+ } else {
+ printf("Error: Stack full. Cannot push %g\n", f);
+ }
+}
+
+double pop(void) {
+ if (sp > 0) {
+ return val[--sp];
+ } else {
+ printf("Error: Stack empty.\n");
+ return 0.0;
+ }
+}
+
+int getop(char s[]) {
+ int i = 0;
+ int c, next;
+
+ while ((s[0] = c = getch()) == ' ' || c == '\t') {
+ }
+ s[1] = '\0';
+ /* The final check is for negative numbers. */
+ if (!isdigit(c) && c != '.' && c != '-') {
+ return c;
+ }
+ /* The second half of this if-statement accounts for negatives */
+ if (c == '-') {
+ next = getch();
+ if (!isdigit(next) && next != '.') {
+ return c;
+ } else {
+ c = next;
+ }
+ } else {
+ c = getch();
+ }
+
+ while (isdigit(s[++i] = c)) {
+ c = getch();
+ }
+ if (c == '.') {
+ while (isdigit(s[++i] = c = getch())) {
+ }
+ }
+ s[i] = '\0';
+ if (c != EOF) {
+ ungetch(c);
+ }
+ return NUMBER;
+}
+
+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;
+ }
+}
+
+void stack_top(void) {
+ if (sp > 0) {
+ printf("Top of stack is %8g\n", val[sp - 1]);
+ } else {
+ printf("Error: Stack empty.\n");
+ }
+}
+
+double dupe_top(void) {
+ double temp = pop();
+ push(temp);
+ push(temp);
+}
+
+void swap_top_two(void) {
+ double tmp1, tmp2;
+ tmp1 = pop();
+ tmp2 = pop();
+ push(tmp1);
+ push(tmp2);
+}
+
+void clear_stack(void) {
+ sp = 0;
+}
--
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