Lowest Common Ancestor in a Binary Search Tree

Here the lowest common ancestor of 12 and 14 is 13 , lca of 1 and 13 is 10 so on . 

#include <stdio.h>

#include <stdlib.h>

struct btnode

{

    int value;

    struct btnode *l;

    struct btnode *r;

}*root = NULL, *temp = NULL, *t2, *t1;

void create()

{

    int data;

    printf("Enter data of node to be inserted : ");

    scanf("%d", &data);

    temp = (struct btnode *)malloc(1*sizeof(struct btnode));

    temp->value = data;

    temp->l = temp->r = NULL;

}

void search(struct btnode *t)

{

    if ((temp->value > t->value) && (t->r != NULL))

        search(t->r);

    else if ((temp->value > t->value) && (t->r == NULL))

        t->r = temp;

    else if ((temp->value < t->value) && (t->l != NULL))

        search(t->l);

    else if ((temp->value < t->value) && (t->l == NULL))

        t->l = temp;

}

void insert()

{

    create();

    if (root == NULL)

        root = temp;

    else

        search(root);

}

void inorder(struct btnode *t)

{

    if (root == NULL)

    {

        printf("No elements in a tree to display");

        return;

    }

    if (t->l != NULL)

        inorder(t->l);

    printf("%d -> ", t->value);

    if (t->r != NULL)

        inorder(t->r);

}

int size(struct btnode* root)

{

    if(root->l==NULL&& root->r==NULL)

        return 1;

    if(root->l!=NULL && root->r==NULL)

        return 1+size(root->l);

    if(root->r!=NULL && root->l==NULL)

        return 1+size(root->r);

  return (size(root->l)+size(root->r))+1;

}

void lowest_common_ancestor(struct btnode* root,int n1,int n2)

{

     if(root->value>n1 && root->value>n2)

    {

        lowest_common_ancestor(root->l,n1,n2);

    }

    if(root->value<n1 && root->value<n2)

    {

        lowest_common_ancestor(root->r,n1,n2);

    }

    if((root->value)<n2 && (root->value)>n1)

    {

        printf("Lowest Common ancestor is %d",root->value);

    }

}

int main()

{

    int ch;

    int a1,a2,num;

    while(1)

    {

    printf("\n");

    printf("OPERATIONS ---\n");

    printf("1.Insert an element into tree\n");

    printf("2.Inorder Traversal\n");

    printf("3.Lowest common Ancestor \n");

    printf("4 Exit\n");

    printf("Enter your choice : ");

    scanf("%d", &ch);

        switch (ch)

        {

        case 1:

            insert();

            break;

        case 2:

            inorder(root);

            break;

        case 3:

            printf("Enter the 2 nodes who's lowest ancestor has to found\n");

            scanf("%d",&a1);

            scanf("%d",&a2);

            lowest_common_ancestor(root,a1,a2);

            break;

        case 4:

            exit(0);

        default :

            printf("Wrong choice, Please enter correct choice  ");

            break;

        }

    }

    return 0;

}