Need help in resolving an error in the attached code

When the below code is executed, it gives an error in the statement below statement.
T=Binary_Tree(list, 0, number);

The error says.
"Non portable pointer assignment in function main". I am using TurboC on win32.




#include<stdio.h>
#include<conio.h>

/* -------------------------------------------------------  */
/* Definitions */

struct node
{
      char info;
      struct node *left_child;
      struct node *right_child;

};

struct node *binary_tree(char *, int, int);
void output(struct node*, int);
void pre_order(struct node*);
void in_order(struct node*);


/* -------------------------------------------------------  */
/* Function to create an binary tree */

struct node * binary_tree (char * list, int lower, int upper)
{
      struct node * node;
      int mid=(lower+upper)/2;

node=(struct node*)malloc(sizeof(struct node));
node->info=list [mid];

if(lower>=upper)
{
      node->left_child=NULL;
      node->right_child=NULL;
      return(node);

}
if(lower<=mid-1)
      node->left_child=binary_tree(list,lower,mid-1);
else
      node->left_child=NULL;
if(mid+1<=upper)
      node->right_child=binary_tree(list,mid+1,upper);
else
      node->right_child=NULL;
      return(node);
}


/* -------------------------------------------------------  */
/* output Function */

void output(struct node *T, int level)
{
      int i;
      if(T)
      {
            output(T->right_child, level+1);
            printf("\n");
            for(i=0;i<level;i++)
                  printf("    ");

            printf(" %c", T->info);
            output(T->left_child,level+1);
      }
}


/* ------------------------------------------------------- */
/* Pre_order Traversal */

void pre_order (struct node *node)
{
      if(node)
      {
            printf("%c", node->info);
            pre_order (node->right_child);
            pre_order(node->right_child);
      }
}


/* ------------------------------------------------------- */
/* In_order traversal */

void in_order(struct node *node)
{
      if(node)
      {
            in_order(node->left_child);
            printf("%c",node->info);
            in_order(node->right_child);
      }
}


/* ------------------------------------------------------- */
/* The entry point - Main */

void main()
{
      char list[100];
      int number = 0;
      char info;
      char choice;
      struct node *T=(struct node*)malloc(sizeof(struct node));
      T=NULL;
      printf("\n Input choice 'b' to break:");
      choice=getchar();
      fflush(stdin);
      while(choice!='b')
      {
            printf("\n Input information of the node:");
            scanf("%c", &info);
            list[number++] = info;
            fflush(stdin);
            printf("\n Input choice 'b' to break:");
            choice=getchar();
            fflush(stdin);
      }
      number--;
      printf("\n number of elements in the list is %d", number);
      T=Binary_Tree(list, 0, number);
      output(T,1);
      printf("\n pre_order traversal\n');
      pre_order(T);
      printf("\n In_order traversal \n");
      in_order(T);