consturcting tree from its preorder,inorder..

[transgalactic]

i have two arrays which represent the preorder
and inorder traversals in two rows.

i cant see why i get an empty tree?

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef struct  node node;
struct node{
	int key;
	node* left;
	node* right;
};


 

node* t(char* pre,char* in,int st_pre,int en_pre,int st_in,int en_in); 
int main ()
{
	
	char pre[13]={'a','b','c','d','e','f','g','h','i','j','k','l','\0'};
	char in[13]={'c','b','e','d','f','a','h','g','j','i','l','k','\0'};
	node* root=t(pre,in,0,0,0,0);

	return 0;
}

node* t(char* pre,char* in,int st_pre,int en_pre,int st_in,int en_in)
{
	int i;
	node* root=(node*)malloc(sizeof(node));
	if (st_pre==en_pre)
		return NULL;
	 
     
	  root->key=pre[st_pre];
	  for(i=0;((i<(int)strlen(pre))&&(pre[st_pre]!=in[i]));i++)
	  {
	  }
	  root->left=t(pre,in,st_pre+1,st_pre+i+1,st_in,i-1);
      root->right=t(pre,in,st_pre+i+1,(int)(strlen(pre)-1),i+1,(int)(strlen(pre)-1));
	  return root;
 
}

[ZuK]

	if (st_pre==en_pre)
		return NULL;

That's why
Kurt