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

#define SIZE 50 /* Size of Stack */

double s[SIZE];
int peak=-1; /* Global declarations */
char pofx[50];

double pop()
{                      /* Function for POP operation */
  return(s[peak--]);
}

double push(double elem) {
  if (peak + 1 >= SIZE) {
    printf("Stack overflown");
    return 0;
  }
  s[++peak] = elem;
}

void main()
{                         /* Main Program */
    printf("Enter the Postfix Expression:");
    // fgets(pofx,100,stdin); // 100??
    fgets(pofx, sizeof pofx, stdin); // better
    postfixtoresult();
    printf("Result: %lfn",s[peak]);
}

void postfixtoresult()
{
  int i=0;
  const char *st = pofx;

  while (*st) {
    char *end; //location to store end of FP parsing
    double value = strtod(st, &end);
    if (end > st) {
      push(value);
      st = end;
    } else if (isspace((unsigned char) *st)) {
      st++;
    } else {
      switch (*st) {
        case '+':push(pop() + pop());break; // pop order irrelevant
        case '-':{ double t = pop(); push(pop() - t);break; } // pop order             relevant
        case '*':push(pop() * pop());break; // pop order irrelevant
        case '/':{ double u = pop(); push(pop() / u);break; }  // pop order relevant
        case '^':{ double v = pop(); push(pow(pop(),v));break; }  // pop order relevant

        default: {
          printf("Input invalid operator: character code %dn", *st);
          return 0;
        }
      }  // end switch
      st++;
    }
  }
}