Building a binary tree in C

The following program shows how to build a binary tree in a C program. It uses dynamic memory allocation, pointers and recursion. A binary tree is a very useful data-structure, since it allows efficient insertion, searching and deletion in a sorted list. As such a tree is essentially a recursively defined structure, recursive programming is the natural and efficient way to handle it.



tree
empty
node left-branch right-branch

left-branch
tree

right-branch
tree

#include
#include

struct tree_el {
int val;
struct tree_el * right, * left;
};

typedef struct tree_el node;

void insert(node ** tree, node * item) {
if(!(*tree)) {
*tree = item;
return;
}
if(item->val<(*tree)->val)
insert(&(*tree)->left, item);
else if(item->val>(*tree)->val)
insert(&(*tree)->right, item);
}

void printout(node * tree) {
if(tree->left) printout(tree->left);
printf("%d\n",tree->val);
if(tree->right) printout(tree->right);
}

void main() {
node * curr, * root;
int i;

root = NULL;

for(i=1;i<=10;i++) { curr = (node *)malloc(sizeof(node)); curr->left = curr->right = NULL;
curr->val = rand();
insert(&root, curr);
}

printout(root);
}