#define SIZE 50
#include <ctype.h>
char s[SIZE];
int top = -1;

push(char elem) {
 s[++top] = elem;
}

char pop() {
 return (s[top--]);
}

int pr(char elem) {
 switch (elem) {
 case '#':
  return 0;
 case '(':
  return 1;
 case '+':
 case '-':
  return 2;
 case '*':
 case '/':
  return 3;
 }
}

main() {
 char infx[50], pofx[50], ch, elem;
 int i = 0, k = 0;
 printf("\n\nRead the Infix Expression ? ");
 scanf("%s", infx);
 push('#');
 while ((ch = infx[i++]) != '\0') {
  if (ch == '(')
   push(ch);
  else if (isalnum(ch))
   pofx[k++] = ch;
  else if (ch == ')') {
   while (s[top] != '(')
    pofx[k++] = pop();
   elem = pop();
  } else {
   while (pr(s[top]) >= pr(ch))
    pofx[k++] = pop();
   push(ch);
  }
 }
 while (s[top] != '#')
  pofx[k++] = pop();
 pofx[k] = '\0';
 printf("\n\nGiven Infix Expn: %s  Postfix Expn: %s\n", infx, pofx);
}