fatal.h

#include <stdio.h>
#include <stdlib.h>

#define Error(Str)        FatalError(Str)
#define FatalError(Str)   fprintf(stderr, "%s\n", Str), exit(1)

tree.h

typedef int ElementType;

#ifndef _Tree_H
#define _Tree_H

struct TreeNode;
typedef struct TreeNode *Position;
typedef struct TreeNode *SearchTree;

SearchTree MakeEmpty(SearchTree T);
Position Find(ElementType X, SearchTree T);
Position FindMin(SearchTree T);
Position FindMax(SearchTree T);
SearchTree Insert(ElementType X, SearchTree T);
SearchTree Delete(ElementType X, SearchTree T);
ElementType Retrieve(Position P);

#endif  

tree.c

#include "tree.h"
#include <stdlib.h>
#include "fatal.h"

struct TreeNode
{
    ElementType Element;
    SearchTree  Left;
    SearchTree  Right;
};

SearchTree MakeEmpty(SearchTree T)
{
    if (T != NULL)
    {
        MakeEmpty(T->Left);
        MakeEmpty(T->Right);
        free(T);
    }
    return NULL;
}

Position Find(ElementType X, SearchTree T)
{
    if (T == NULL)
        return NULL;
    if (X < T->Element)
        return Find(X, T->Left);
    else if (X > T->Element)
        return Find(X, T->Right);
    else
        return T;
}

Position FindMin(SearchTree T)
{
    if (T == NULL)
        return NULL;
    else if (T->Left == NULL)
        return T;
    else
        return FindMin(T->Left);
}

Position FindMax(SearchTree T)
{
    if (T != NULL)
    {
        while (T->Right != NULL)
            T = T->Right;
    }
    return T;
}

SearchTree Insert(ElementType X, SearchTree T)
{
    if (T == NULL)
    {
        /* Create and return a one-node tree */
        T = malloc(sizeof(struct TreeNode));
        if (T == NULL)
            FatalError("Out of space!!!");
        else
        {
            T->Element = X;
            T->Left = T->Right = NULL;
        }
    }
    else if (X < T->Element)
        T->Left = Insert(X, T->Left);
    else if (X > T->Element)
        T->Right = Insert(X, T->Right);
    /* Else X is in the tree already; we'll do nothing */

    return T;  /* Do not forget this line!! */
}

SearchTree Delete(ElementType X, SearchTree T)
{
    Position TmpCell;

    if (T == NULL)
        Error("Element not found");
    else if (X < T->Element)  /* Go left */
        T->Left = Delete(X, T->Left);
    else if (X > T->Element)  /* Go right */
        T->Right = Delete(X, T->Right);

    /* Found element to be deleted */
    else if (T->Left && T->Right)  /* Two children */
    {
        /* Replace with smallest in right subtree */
        TmpCell = FindMin(T->Right);
        T->Element = TmpCell->Element;
        T->Right = Delete(T->Element, T->Right);
    }
    else  /* One or zero children */
    {
        TmpCell = T;
        if (T->Left == NULL) /* Also handles 0 children */
            T = T->Right;
        else if (T->Right == NULL)
            T = T->Left;
        free(TmpCell);
    }

    return T;
}

ElementType Retrieve(Position P)
{
    return P->Element;
}

testtree.c

#include "tree.h"
#include <stdio.h>

int main()
{
    SearchTree T;
    Position P;
    int i;
    int j = 0;

    T = MakeEmpty(NULL);
    for (i = 0; i < 50; i++, j = (j + 7) % 50)
        T = Insert(j, T);
    for (i = 0; i < 50; i++)
        if ((P = Find(i, T)) == NULL || Retrieve(P) != i)
            printf("Error at %d\n", i);

    for (i = 0; i < 50; i += 2)
        T = Delete(i, T);

    for (i = 1; i < 50; i += 2)
        if ((P = Find(i, T)) == NULL || Retrieve(P) != i)
            printf("Error at %d\n", i);
    for (i = 0; i < 50; i += 2)
        if ((P = Find(i, T)) != NULL)
            printf("Error at %d\n", i);

    printf("Min is %d, Max is %d\n", Retrieve(FindMin(T)),
        Retrieve(FindMax(T)));

    return 0;
}