General - Please help me out with this Binarty Tree C code

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

typedef struct b_node bnode;

struct b_node{
bnode *left;
bnode *right;
int id;
};

typedef bnode* bst;

bst readVal()
{
int num;
int ctr=1;
bnode *cur=(bnode*)malloc(sizeof(bnode));
cur=NULL;
bst top=cur;
fscanf(stdin,"%d",&num);
while(num!=0)
{
bnode *newn=(bnode*)malloc(sizeof(bnode));
newn->id=num;
newn->left=NULL;
newn->right=NULL;
next:
if(cur==NULL)
{

cur=newn;

printf("\nFirst node created\n");
free(newn);
fscanf(stdin,"%d",&num);
continue;
}
else
{
printf("\nNode %d Creating ",ctr);
cur=top;
if(num>cur->id)
cur=cur->right;
else
cur=cur->left;
goto next;
}

fscanf(stdin,"%d",&num);
}
printf("\nTree created\n");
return top;
}

int countnodes(bnode *tree)
{
if(tree==NULL)
return 0;
else
return 1+countnodes(tree->left)+countnodes(tree->right);
}

int main()
{
bnode *tree=(bnode*)malloc(sizeof(bnode));
tree=readVal();
int num;
num=countnodes(tree);
printf("No. of nodes : %d ",num);
}



I am getting segmentation fault after the creation of the first node.

This is a bit weird:
bnode *cur=(bnode*)malloc(sizeof(bnode));
cur=NULL;

You're allocating memory and then never using it.

Besides that, as far as I can see, you're creating newn, then setting cur to point to it, then freeing it, then setting cur to top, which is still pointing at NULL. Which is bad.