소스코드에는 문제가 없는데 실행시켜서 값을 입력하면 중단이 됩니다....

#include <stdio.h>
#include <stdlib.h>
 
 
typedef struct TreeNode
{
 char data;
 struct TreeNode *left, *right;
}TreeNode;
 
#define MAX_STACK_SIZE 100
 
typedef TreeNode* element;
 
typedef struct
{
 element stack[MAX_STACK_SIZE];
 int top;
}StackType;
 
element push(StackType *s, TreeNode *p)
{
 s->top++;
 
 return s->stack[s->top] = p;
 
}
 
element pop(StackType *s)
{
 s->top--;
 return s->stack[s->top];
}
 
TreeNode * makeET(char *expr, StackType *s)
{
 char ch;
 TreeNode *p;
 
 while(*expr != '\0')
 {
  ch = *expr;
 
  switch(ch)
  {
   case '+':
   case '-':
   case '*':
   case '/':
    p = (TreeNode*)malloc(sizeof(TreeNode));
    p->data = ch;
    p->right = pop(s);
    p->left = pop(s);
    push(s, p);
    break;
 
   default:
    p = (TreeNode*)malloc(sizeof(TreeNode));
    p->data = ch;
    p->right = NULL;
    p->left = NULL;
    push(s,p);
    break;
  }
 }
 return p;
}
 
 
 
void inorder(TreeNode *p)
{
 if(p != NULL)
 {
  inorder(p->left);
  printf("%d", p->data);
  inorder(p->right);
 }
}
 
void preorder(TreeNode *p)
{
 if( p != NULL)
 {
  printf("%d", p->data);
  preorder(p->left);
  preorder(p->right);
 }
}
 
void postorder(TreeNode *p)
{
 if(p != NULL)
 {
  postorder(p->left);
  postorder(p->right);
  printf("%d", p->data);
 }
}
 
 
int main(void)
{
 StackType s;
 TreeNode* p;
 char expr[10];
 s.top = -1;
 
 
 printf("input expr :");
 scanf("%s", expr);
 
 
 p = makeET(expr, &s);
 
 inorder(p);
 preorder(p);
 postorder(p);
 
}