finding_postfix expression _in_C

#include <stdio.h>
#include <stdlib.h>
#include<math.h>
#define SIZE 20
int STACK[SIZE], top = -1;

void push(int item)
{
  if(top == SIZE-1)
    printf("\nSTACK OVERFLOWED");
  else
  {
    top++;
    STACK[top] = item;
  }
}

int pop()
{
  if(top == -1)
    printf("STACK UNDERFLOWED");
  else
  {
    return STACK[top--];
  }
}

int main(void) 
{
  char postfix[SIZE];
  int i = 0, a, b, c;
  printf("\nEnter the POSTFIX Expression : ");
  scanf("%s", postfix);

  while(postfix[i] != '\0')
  {
    if(postfix[i] >='0' && postfix[i] <= '9')
    {
      int n = postfix[i]-48;
      push(n);
    }
    else if(postfix[i] ==  '+' || postfix[i] ==  '-' || postfix[i] ==  '*' || postfix[i] ==  '/' || postfix[i] ==  '^')
    {
      a = pop();
      b = pop();
      switch(postfix[i])
      {
        case '+' : 
          c = b+a;
          push(c);
          break;

        case '-' : 
          c = b-a;
          push(c);
          break;

        case '*' : 
          c = b*a;
          push(c);
          break;

        case '/' : 
          c = b/a;
          push(c);
          break;

        case '^' : 
          c = pow(b,a);
          push(c);
          break;
      }
    }
    i++;
  }

  printf("Result is %d ", STACK[top]);
  return 0;
}