Page 159

Rewrite the postfix calculator of Chapter 4 to use scanf and/or sscanf to do the input and number conversion.

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

#define LOWVAR 'a'
#define HIGHVAR 'z'
#define MAXOP 100
#define NUMBER '0'

int getterm(char[]);
void push(double);
double pop(void);
void clear(void);
void assign(char, double);
double fetch(char);

int main()
{
int type;
double op, op2;
char s[MAXOP];

while (getterm(s) != EOF) {
if (s[0] == '\n') {
printf("\t%.8g\n", pop());
} else if (sscanf(s, "%lg", &op)) {
push(op);
} else if (sscanf(s, "%c", s)) {
switch (s[0]) {
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 '#': // print top element
break;
case '&': // duplicate top element
break;
case '~': // swap top two elements
op = pop();
op2 = pop();
push(op);
push(op2);
break;
case '!': // clear the stack
clear();
break;
case '\$':
push(sin(pop()));
break;
case '?':
push(exp(pop()));
break;
case '^':
op2 = pop();
push(pow(op2, pop()));
break;
case '\n':
break;
}
}
}

return 0;
}

#include <ctype.h>

int getch(void);
void ungetch(int);
int getterm(char out[])
{
char *p = out;

while (isspace(*p = getch()) && *p != '\n')
;

if (*p == EOF || *p == '\n') {
return *p;
}

while (!isspace(*++p = getch()))
;

ungetch(*p);

*p = '\0';
return out[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;
}

#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;
}
}

double vars[HIGHVAR - LOWVAR];

void assign(char c, double d)
{
vars[c - LOWVAR] = d;
}

double fetch(char c)
{
return vars[c - LOWVAR];
}
``````