Unable to print elements in binary search tree - c

Question

My code is not printing the elements of binary search tree:
//x is the element to be inserted
//structure of program
typedef struct BST
{
int info;
struct BST *left;
//pointer to left node
struct BST *right;
//pointer to right node
}
bst;
//global root variable
bst *root;
void insert(int x)
{
bst *ptr,*sptr=root;
ptr=(bst*)malloc(sizeof(bst));
ptr->info=x;
if(root==NULL)
{
ptr->left=ptr->right=NULL;
root=ptr;
}
while(sptr!=NULL)
{
if(x<sptr->info)
{
sptr=sptr->left;
}
else
sptr=sptr->right;
}
sptr=ptr;
}
edit:
//following is the show function
void show()
{
bst *ptr=root;
while(ptr!=NULL)
{
//it will print untill the ptr is null
printf("%d",ptr->info);
ptr=ptr->left;
ptr=ptr->right;
}
}

Answer 1

Where is the value of root coming from? You're not passing in the value anywhere? Also, it is tough to help when we don't know the design of type bst.
It appears that you have the right idea. Create a node, and give it some data. If the root is null, then the new value is the root of the BST. After that you go ahead and find the first null node either in the left or right subtree of the root using the standard BST behavior. Finally, when you reach the end you go ahead and insert the last node in the proper place.
void insert(int x)
{
bst *ptr, *sptr=root; //<-- the value right here?
ptr = malloc(sizeof(bst));
ptr->info = x;
if(root == NULL)
{
ptr->left=ptr->right=NULL;
root=ptr;
}
while(sptr!=NULL)
{
if(x<sptr->info)
{
sptr=sptr->left;
}
else
sptr=sptr->right;
}
sptr=ptr; // <-- What is this line trying to do?
}
However, where did your updated tree go?
Since in C everything is passed by value, you're running into the problem where you're not seeing your updated tree after you leave this function. You need to go ahead and change the function to return a bst* type, and also maintain the root node during the entire function. Now the first line of code (*sptr = root) makes more sense! Finally, you were not setting the left and right fields of ptr to NULL. This means you were jumping over your if statements.
bst* insert(int x, bst *root)
{
bst *ptr, *sptr=root;
ptr = malloc(sizeof(bst));
ptr->left = NULL;
ptr->right = NULL;
ptr->info = x;
if(root == NULL)
{
ptr->left=ptr->right=NULL;
root=ptr;
return root;
}
while(sptr!=NULL)
{
if(x<sptr->info)
{
sptr=sptr->left;
}
else
sptr=sptr->right;
}
sptr=ptr;
return root;
}
What about the next function?
I just started looking at this one too. I am not used to the global variables in c, so I will go ahead and make two modifications. Let's make this recursive, and pass in the value of the root rather than using the global.
void show(bst *root)
{
if(root == NULL){
return;
}
printf("%d",root->info);
show(root->left);
show(root->right);
}
This will take in some value, and solve the tree recursively, and print as it reaches each node. Thus, it will print the root node (if it exists), and then print the left entire left subtree before it prints the right subtree.
Finally, looking at your main
I added the local variable root and thus you will have to remove the global variable named root outside of your main function. I also set the value of it to null so your first insert will fire correctly.
int main()
{
int i,n,x;
bst *root = NULL; //<-- I added this line of code to remove the global
puts("Enter number of elements");
scanf("%d",&x);
for(i=0;i<x;i++)
{
puts("Enter elements");
scanf("%d",&n);
root = insert(n, root);
}
show(root);
return 0;
}
I hope this helps!