#include <stdio.h>
#include <stdbool.h>

struct Node { int key; const struct Node *left; const struct Node *right; };
static bool contains(const struct Node *node, int key) {
    while (node != NULL) {
        if (key == node->key) { return true; }
        node = key < node->key ? node->left : node->right;
    }
    return false;
}

int main(void) {
    struct Node low = {12, NULL, NULL};
    struct Node high = {30, NULL, NULL};
    struct Node root = {20, &low, &high};
    printf("Found 30: %d\n", contains(&root, 30));
    printf("Found 25: %d\n", contains(&root, 25));
    return 0;
}