Inorder, Preorder and Post-Order traversal of tree

The need:

     This program is written to show the program implementation of the concept explained in the previous post. This program is the implementation of 2 + 3 example given there.

The code:

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#include<stdio.h>
#include<stdlib.h>
struct tree
{
    char num;
    struct tree *left, *right, *parent;
};
typedef struct tree node;

void in_print(node *p);
void pre_print(node *p);
void post_print(node *p);
node * create_node(char c);
int main()
{
    int i;
    node *root=NULL;
    root = create_node('+');
    root->left = create_node('a');
    root->right = create_node('b');
    printf("Pre order print\t\t");
    pre_print(root);
    printf("\nIn order print\t\t");
    in_print(root);
    printf("\nPost order print\t");
    post_print(root);
    putchar('\n');
    return 0;
}

node * create_node(char c)
{
    node *new_node;
    new_node = (node *)malloc(sizeof(node));
    new_node->num = c;
    new_node->parent = NULL;
    new_node->left = NULL;
    new_node->right = NULL;
    return new_node;
}

void pre_print(node *p)
{
    if(p==NULL)
    return;
    else
    printf("%c ",p->num);
    pre_print(p->left);
    pre_print(p->right);
}

void in_print(node *p)
{
    if(p==NULL)
    return;
    else
    in_print(p->left);
    printf("%c ",p->num);
    in_print(p->right);
}

void post_print(node *p)
{
    if(p==NULL)
    return;
    else
    post_print(p->left);
    post_print(p->right);
    printf("%c ",p->num);
}

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Approach:
    This program is just to show the printing of a tree in pre-order, inorder and post order. For that first we have to make the tree. Here I have not created a bigger tree. Here we have the simplest tree with 3 nodes only. So we need not make a function to construct the tree. Here simply I have created 3 nodes and put them to make a small tree. create_node() function creates a node with given data/value ans returns it address. we create first node, make it root. After that we create 2 more nodes and make them left and right children of root. Then there are 3 functions in_print(), pre_print() and post_print() which print the expression in infix, prefix and postfix form respectively.
Remarks:

1. Here this program is shown to print the simplest expression in prefix, infix and post-fix form but this program can be used to print any binary tree in pre-order, inorder and post order.

2. This program is the base of all the tree programs related to trees.