[varun agarwal]

#include <stdio.h>

#include <stdlib.h>

#include <ctype.h>

#include <setjmp.h>

#include <math.h>

char *pb, *p;

jmp_buf env;

double eval() {

  double x;  char *q1, *q2;

  if (isspace(*--p)) {

    while (p>pb && isspace(*p)) --p;

    if (p>pb) switch (*p) {

        case '+': return eval()+eval();

        case '*': return eval()*eval();

        case '-': return x=eval(),eval()-x;

        case '/': return x=eval(),eval()/x;

case 'sin' : return sin(eval());

case 'cos' : return cos(eval());

case 'tan' : return tan(eval());

case 'sqrt' : return sqrt(eval());

case 'pow' : return x=eval(),pow(eval(),x);

//case 'dup' : x=eval(); return x,x;

//case 'swap' : x=eval(), y=eval()); return y,x

case 'print' : return eval();

case 'quit' : return 0;

default:  q1 = p+1;

                  while (!isspace(*--p)) ;

 if (x=strtod(++p,&q2),q2==q1) return x;

    }

  }

  longjmp(env,0);

}

int main() {

  int sz,c,n;

  double x;

  pb = malloc(sz=4);

  *pb = ' ';

  p = pb+1;

  while ((c=getchar())!=EOF)

    if (c!='\n') {

      n = p-pb;

      if (n+2==sz) pb = realloc(pb,sz*=2);

      p = pb+n;

      *p++ = c;

    } else {

      while (--p>pb && isspace(*p)) ;

      if (p++>pb) {

        *p++ = ' ';

        if (!setjmp(env)) {

          x = eval();

          while (--p>pb && isspace(*p)) ;

          if (p>pb)  longjmp(env,0);

          printf("%f\n",x);

        }

        else  printf("error\n");

        p = pb+1;

      }

    }

}

Just check this , also will have to modify a little for dup,swap,pop

--

Varun Agarwal

[Shrey Shankar]

I dont know the exact syntax of C, but swapping of top two elements, the algorithm goes like this

Stack stack = new Stack():
int first = stack.pop():
int second = stack.pop();

stack.push(second);
stack.push(first);

Anyway, you can find the part of your program on this link
http://www.learntosolveit.com/cprogramming/Ex_4.4_rpn_top_two_elements.html

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[manoj kumar]

Hahaha ..