In-order, Pre-order and Post-order Tree Traversal using C Programming

In the last post, I showed you how to implement a Binary Search Tree. In this post, I am going to show you how to traverse a tree using In-order, Pre-order and Postorder traversal method.

In-order traversal method:
1. Visit Left Sub-Tree
2. Process Current Node
3. Visit Right Sub-Tree

Pre-order traversal method:
1. Process Current Node
2. Visit Left Sub-Tree
3. Visit Right Sub-Tree

Post-order traversal method:
1. Visit Left Sub-Tree
2. Visit Right Sub-Tree
3. Process Current Node

C/C++ Implementation with full program:

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

struct node
{
    int value;
    node* left;
    node* right;
};


struct node* root;

struct node* insert(struct node* r, int data);
void inOrder(struct node* r);
void preOrder(struct node* r);
void postOrder(struct node* r);

int main()
{
    root = NULL;
    int n, v;

    printf("How many data's do you want to insert ?\n");
    scanf("%d", &n);

    for(int i=0; i<n; i++){
        printf("Data %d: ", i+1);
        scanf("%d", &v);
        root = insert(root, v);
    }

    printf("Inorder Traversal: ");
    inOrder(root);
    printf("\n");

    printf("Preorder Traversal: ");
    preOrder(root);
    printf("\n");

    printf("Postorder Traversal: ");
    postOrder(root);
    printf("\n");


    return 0;
}

struct node* insert(struct node* r, int data)
{
    if(r==NULL)
    {
        r = (struct node*) malloc(sizeof(struct node));
        r->value = data;
        r->left = NULL;
        r->right = NULL;
    }
    else if(data < r->value){
        r->left = insert(r->left, data);
    }
    else {
        r->right = insert(r->right, data);
    }
    return r;

}

void inOrder(struct node* r)
{
    if(r!=NULL){
        inOrder(r->left);
        printf("%d ", r->value);
        inOrder(r->right);
    }
}

void preOrder(struct node* r)
{
    if(r!=NULL){
        printf("%d ", r->value);
        preOrder(r->left);
        preOrder(r->right);
    }
}

void postOrder(struct node* r)
{
    if(r!=NULL){
        postOrder(r->left);
        postOrder(r->right);
        printf("%d ", r->value);

    }
}