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Add access to library functions like `sin`, `exp`, and `pow`. See `<math.h>` in Appendix B, Section 4.

``````#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define MAXOP 100
#define NUMBER '0'

int getop(char[]);
void push(double);
double pop(void);
void clear(void);

int main()
{
int type;
double op, 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: zero divisor\n");
}
break;
case '%':
op2 = pop();
if (op2 != 0.0) {
push((int)pop() % (int)op2);
} else {
printf("error: zero divisor\n");
}
break;
case 'o': // print top element
break;
case 'd': // duplicate top element
break;
case 'w': // swap top two elements
op = pop();
op2 = pop();
push(op);
push(op2);
break;
case 'q': // clear the stack
clear();
break;
case 's':
push(sin(pop()));
break;
case 'c':
push(cos(pop()));
break;
case 't':
push(tan(pop()));
break;
case 'e':
push(exp(pop()));
break;
case 'p':
op2 = pop();
push(pow(op2, pop()));
break;
case '\n':
printf("\t%.8g\n", pop());
break;
default:
printf("error: unknown comand %s\n", s);
break;
}
}
return 0;
}

#define MAXVAL 100

int sp = 0;
double val[MAXVAL];

void push(double f)
{
if (sp < MAXVAL) {
val[sp++] = f;
} else {
printf("push error: stack full, can't push %g\n", f);
}
}

double pop(void)
{
if (sp > 0) {
return val[--sp];
} else {
printf("pop error: stack empty\n");
return 0.0;
}
}

{
if (sp > 0) {
return val[sp - 1];
} else {
return 0.0;
}
}

void clear(void)
{
sp = 0;
}

#include <ctype.h>

int getch(void);
void ungetch(int);

int getop(char s[])
{
int i = 0, c;

/* Get first char, return if non-numeric */
while ((s[0] = c = getch()) == ' ' || c == '\t')
;

if (!isdigit(c) && c != '.' && c != '-' && c != '+') {
while ((s[++i] = c = getch()) != ' ' && c != '\t'))
;
return c;
}

/* Handle negative or positive sign */
if (c == '-' || c == '+') {
if (!isdigit(s[++i] = c = getch())) {
ungetch(s[i--]);
s[1] = '\0';
return s[0];
}
}

/* Fetch numeric string */
if (isdigit(c)) {
while (isdigit(s[++i] = c = getch()))
;
}
if (c == '.') {
while (isdigit(s[++i] = c = getch()))
;
}
s[i] = '\0';

/* Unget the last unread char */
if (c != EOF) {
ungetch(c);
}

/* Return number indicator */
return NUMBER;
}

#define BUFSIZE 100
char buf[BUFSIZE];
int bufp = 0;

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;
}
}
``````