check if subtree of a binary tree is bst in C code example

Example: how to check if a binary tree is a BST

1    def checkBST(t) 
2        return false if t==nil
3       if t.left!=nil && t.left>t 
4            return false
5        end
6        if t.right!=nil && t.right<t
7            return false
8        end
9        if checkBST(t.left) && checkBST(t.right)
10            return true
11        end
12    end