수식 트리 계산 프로그램

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>

typedef struct TreeNode {
 int data;
 struct TreeNode *left, *right;
} TreeNode;

TreeNode n1 = {1, NULL, NULL};
TreeNode n2 = {4, NULL, NULL};
TreeNode n3 = {'*', &n1, &n2};
TreeNode n4 = {16, NULL, NULL};
TreeNode n5 = {25, NULL, NULL};
TreeNode n6 = {'+', &n4, &n5};
TreeNode n7 = {'+', &n3, &n6};
TreeNode *exp = &n7;

int evaluate(TreeNode *root)
{
 if(root == NULL)
  return 0;
 if(root->left == NULL && root->right == NULL)
  return root->data;
 else {
  int op1 = evaluate(root->left);
  int op2 = evaluate(root->right);

  switch(root->data) {
  case '+' :
   return op1+op2;
   case '-' :
   return op1-op2;
   case '*' :
   return op1*op2;
   case '/' :
   return op1/op2;
  }
 }
 return 0;
}

void main()
{
 printf("%d\n", evaluate(exp));
}