Write C code to check if a given binary tree is a binary search tree or not?

Here is a C program which checks if a given tree is a Binary Search Tree or not...

int isThisABST(struct node* mynode) 

{ 

    if (mynode==NULL) return(true); 

    if (node->left!=NULL && maxValue(mynode->left) > mynode->data) 

       return(false);

    if (node->right!=NULL && minValue(mynode->right) <= mynode->data) 

       return(false); 

    if (!isThisABST(node->left) || !isThisABST(node->right)) 

       return(false); 


    return(true); 

}