Binary Tree is BST or not c++

#include <iostream>
#include <limits.h>
using namespace std;
struct node
{
int  data;
node *left,*right;
};

void print(node *t)
{
if(t!=NULL)
{
print(t->left);
cout<<t->data<<" ";
print(t->right);

}

}

node * create(int  a)
{
node *t=new node;
t->data=a;
t->left=t->right=NULL;
return t;
}
int isBST(node *t,int min,int max)
{
if(t==NULL)return 1;
if(t!=NULL)
{
if(t->data<min||t->data>max)
return 0;
}

return (isBST(t->left,min,t->data)&&isBST(t->right,t->data,max));
}
int main()
{
node *t=NULL;
t=create(4);
t->left=create(2);
t->right=create(1);
print(t);
if(isBST(t,INT_MIN,INT_MAX))
cout<<" BST \n";
else cout<< "not BST\n";

return 0;
}