exercise 4.04-4.06

chapter_4/exercise_4_04.c

@@ -0,0 +1,56 @@
+#include <stdio.h>
+
+void push(double);
+double pop(void);
+double peek(void);
+void clear();
+
+int main()
+{
+    push(1.0);
+    push(2.0);
+    push(3.0);
+    printf("peek: %f\n", peek());
+    clear();
+    pop();
+}
+
+#define MAXVAL 100
+int sp = 0;
+double val[MAXVAL];
+
+/* push: push f onto value stack */
+void push(double f)
+{
+    if (sp < MAXVAL) {
+        val[sp++] = f;
+    } else {
+        printf("error: stack full, can't push %g\n", f);
+    }
+}
+
+/* pop: pop and return top value from stack */
+double pop(void)
+{
+    if (sp > 0) {
+        return val[--sp];
+    } else {
+        printf("error: stack empty\n");
+        return 0.0;
+    }
+}
+
+double peek(void)
+{
+    if (sp > 0) {
+        return val[sp - 1];
+    } else {
+        printf("error: stack empty\n");
+        return 0.0;
+    }
+}
+
+void clear(void)
+{
+    sp = 0;
+}

chapter_4/exercise_4_05.c

@@ -0,0 +1,138 @@
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+#define MAXOP  100 /* max size of operand or operator */
+#define NUMBER '0' /* signal that a number was found */
+
+int getop(char[]);
+void push(double);
+double pop(void);
+
+int getch(void);
+void ungetch(int);
+
+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());
+        case '-':
+            op2 = pop();
+            push(pop() - op2);
+            break;
+        case '/':
+            op2 = pop();
+            if (op2 != 0.0) {
+                push(pop() / op2);
+            } else {
+                printf("error: zero divisor\n");
+            }
+            break;
+        case 's':
+            push(sin(pop()));
+            break;
+        case 'e':
+            push(exp(pop()));
+            break;
+        case 'p':
+            op2 = pop();
+            push(pow(pop(), op2));
+            break;
+        case '\n':
+            printf("\t%.8g\n", pop());
+            break;
+        default:
+            printf("error: unkown command %s\n", s);
+            break;
+        }
+    }
+
+    return 0;
+}
+
+#define MAXVAL 100
+int sp = 0;
+double val[MAXVAL];
+
+/* push: push f onto value stack */
+void push(double f)
+{
+    if (sp < MAXVAL) {
+        val[sp++] = f;
+    } else {
+        printf("error: stack full, can't push %g\n", f);
+    }
+}
+
+/* pop: pop and return top value from stack */
+double pop(void)
+{
+    if (sp > 0) {
+        return val[--sp];
+    } else {
+        printf("error: stack empty\n");
+        return 0.0;
+    }
+}
+
+int getop(char s[])
+{
+    int i, c;
+    while ((s[0] = c = getch()) == ' ' || c == '\t') {
+    }
+
+    s[1] = '\0';
+    if (!isdigit(c) && c != '.')
+        return c;
+
+    i = 0;
+
+    if (isdigit(c)) {
+        while (isdigit(s[++i] = c = getch())) {
+        }
+    }
+    if (c == '.') {
+        while (isdigit(s[++i] = c = getch())) {
+        }
+    }
+
+    s[i] = '\0';
+
+    if (c != EOF) {
+        ungetch(c);
+    }
+
+    return NUMBER;
+}
+
+#define BUFSIZE 100
+
+char buf[BUFSIZE]; /* buffer for ungetch */
+int bufp = 0;      /* next free position in buf */
+
+int getch(void)
+{
+    return (bufp > 0) ? buf[--bufp] : getchar();
+}
+
+void ungetch(int c) /* push character back on input */
+{
+    if (bufp >= BUFSIZE) {
+        printf("ungetch: too many characters\n");
+    } else {
+        buf[bufp++] = c;
+    }
+}