infix to postfix

#include <stdio.h>
char stack[50];
int top=-1;
int pop()
{
  return stack[top--];
}
void push(char x)
{
  stack[++top]=x;
}
int prio(char ch)
{  int p;
  switch(ch)
    {
      case '*':
      case '/':
      p=2;break;
      case '+':
      case '-':
      p=1;
      break;
      case '(':
      p=-1;
      break;
    }
 return p;
}
void conversion(char infix[],char postfix[])
{int k=0;
  int i=0;
  char p;
  while(infix[i]!='\0')
    {char p=infix[i];
     switch(p)
       {
         default:
         postfix[k++]=p;
         break;
         case '(':
         push(p);
         break;
         case ')':
         while(top!=-1&&stack[top]!='(')
           postfix[k++]=pop();
         pop();
         break;
         case '+':
         case '-':
         case '*':
         case '/':
         while(top!=-1&&prio(stack[top])>=prio(p))
           {
             postfix[k++]=pop();
             
             
           }
         push(p);
         break;
         
       }
        
      
    i++;}
 while(top!=-1)
   {
     postfix[k++]=pop();
   }
 postfix[k]='\0';
}
int main()
{
  char infix[50],postfix[50];
  printf("enter the expression\n");
  scanf("%s",infix);
  conversion(infix,postfix);
  printf("postfix  %s",postfix);
}