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4.05.c
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4.05.c
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/* vim: set sw=4 ts=4:
* Author: Liu DongMiao <liudongmiao@gmail.com>
* Created : Fri 10 Aug 2012 10:24:39 AM CST
* Modified : Mon 13 Aug 2012 03:04:26 PM CST
*/
/*
* Add access to library functions like ``sin'', ``exp'', and ``pow''. See
* <math.h> in Appendix B, Section 4.
*/
#include <stdio.h>
#include <stdlib.h>
#ifndef ORIGINAL
#include <math.h>
#define SIN 's'
#define EXP 'e'
#define POW 'p'
#endif
#define MAXOP 100
#define NUMBER '0'
int getop(char []);
void push(double);
double pop(void);
/* reverse Polish calculator */
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: zero divisor\n");
break;
#ifndef ORIGINAL
case '%':
op2 = pop();
if ((int)op2 != 0)
push((int)pop() % (int)op2);
else
printf("error: zero modulus\n");
break;
case SIN:
push(sin(pop()));
break;
case EXP:
push(exp(pop()));
break;
case POW:
op2 = pop();
push(pow(pop(), op2));
break;
#endif
case '\n':
printf("\t%.8g\n", pop());
break;
default:
printf("error: unknown command %s\n", s);
break;
}
}
return 0;
}
#define MAXVAL 100 /* maximum depth of val stack */
int sp = 0; /* next free stack position */
double val[MAXVAL]; /* value stack */
/* 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;
}
}
#include <ctype.h>
int getch(void);
void ungetch(int);
/* getop: get next character or numeric operand */
int getop(char s[])
{
int i, c;
while ((s[0] = c = getch()) == ' ' || c == '\t')
;
s[1] = '\0';
#ifdef ORIGINAL
if (!isdigit(c) && c != '.')
return c; /* not a number */
i = 0;
#else
/* sin */
if (c == 's') {
if ((c = getch()) != 'i') {
ungetch(c);
} else if ((c = getch()) != 'n') {
ungetch(c);
}
s[1] = 'i';
s[2] = 'n';
s[3] = '\0';
return SIN;
}
/* exp */
if (c == 'e') {
if ((c = getch()) != 'x') {
ungetch(c);
} else if ((c = getch()) != 'p') {
ungetch(c);
}
s[1] = 'x';
s[2] = 'p';
s[3] = '\0';
return EXP;
}
/* pow */
if (c == 'p') {
if ((c = getch()) != 'o') {
ungetch(c);
} else if ((c = getch()) != 'w') {
ungetch(c);
}
s[1] = 'o';
s[2] = 'w';
s[3] = '\0';
return POW;
}
if (!isdigit(c) && c != '.' && c != '-')
return c;
i = 0;
if (c == '-') {
c = getch();
if (!isdigit(c) && c != '.') {
ungetch(c);
return '-';
}
s[++i] = c;
}
#endif
if (isdigit(c)) /* collect integer part */
while (isdigit(s[++i] = c = getch()))
;
if (c == '.') /* collect fraction part */
while (isdigit(s[++i] = c = getch()))
;
s[i] = '\0';
if (c != EOF)
ungetch(c);
return NUMBER;
}
#define BUFSIZE 100
char buf[BUFSIZE];
int bufp = 0;
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;
}