infix expression to postfix expression

#include<conio.h>
#include<stdio.h>
#include<stdlib.h>
#define max 30


char stack[max];
int top=-1;


void push(char item)
{
stack[++top]=item;
}


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


int priority(char item)
{
switch(item)
 {
 case '(':return 1;
 case '+':
 case '-':return 2;
 case '*':
 case '/':return 3;
 default:return 0;
 }
}

void main()
{
char infx[50],pofx[50],ch,item;
int i=0,k=0;
clrscr();
printf("\n Read infix expression:");
scanf("%s",infx);
push('(');
while(infx[i]!='\0')
 {
  ch=infx[i++];
  if(ch=='(')
  push(ch);
  else if(isalnum(ch))
  pofx[k++]=ch;
  else if(ch==')')
   {
    while(stack[top]!='(')
    pofx[k++]=pop();
    pop();
   }
   else
   {
   while(priority(stack[top])>=priority(ch))
   pofx[k++]=pop();
   push(ch);
   }
 }
   while(top!=-1)
   pofx[k++]=pop();
   pofx[k]='\0';
   printf("Postfix is=%s",pofx);
   getch();

}