Exercise 4-4. Add the commands to print the top elements of the stack without popping, to duplicate it, and to swap the top two elements. Add a command to clear the stack.
#include <stdio.h>
#include <stdlib.h> //for atof()
#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);
void clear(void);
/* reverse polish calculator */
int main()
{
int type;
double op1, 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)
push(pop() / op2);
else
printf("error: zero devisior\n");
break;
case '%':
op2 = pop();
if(op2 != 0.0)
push(fmod(pop(), op2));
else
printf("error: zero devisor\n");
break;
case '?':
op2 = pop();
printf("\t%.8g\n", op2);
push(op2);
break;
case 'd': //double
op2 = pop();
push(op2);
push(op2);
break;
case 'r': //reverse
op1 = pop();
op2 = pop();
push(op1);
push(op2);
break;
case 'c': //clean
clear();
break;
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
double val[MAXVAL]; //value stack
int sp = 0; //next free stack position
/* push: push f into 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;
}
}
/* clear */
void clear(void)
{
sp = 0;
}
#include <ctype.h>
int getch(void);
void ungetch(int);
/* getop: get next character ot numeric operand */
int getop(char s[])
{
int i, c;
while((s[0] = c = getch()) == ' ' || c == '\t')
;
s[1] = '\0';
if(!isdigit(c) && c != '.' && c != '-') // not a number
return c;
i = 0;
if (c == '-')
{
if(isdigit(c = getch()) || c == '.')
s[++i] = c; //negative numbers
else
{
if(c != EOF)
ungetch(c);
return '-';
}
}
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]; //buffer for ungetch;
int bufp = 0; //next free position in buf
int getch(void) // get a (possibly pushed-back) character
{
return (bufp > 0) ? buf[--bufp] : getchar();
}
void ungetch(int c) // push character back on input
{
if(bufp >= BUFSIZE)
printf("ungetch: too many characnters\n");
else
buf[bufp++] = c;
}
Result:
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