NULL
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malloc
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#include <stdlib.h> /* * Declare a binary tree of integers */ struct s_tree { int val; struct s_tree *left, *right; }; main() { struct s_tree *tree, *node; node = (struct s_tree *)malloc(sizeof(struct s_tree)); node->val = 5; node->left = node->right = NULL; tree = node; node = (struct s_tree *)malloc(sizeof(struct s_tree)); node->val = 12; node->left = node->right = NULL; tree->right = node; }