Segmentation fault upon insertion into binary search tree - c

Question

I wrote the following code to insert into binary search tree which can have duplicate entries but i get segmentation fault for larger inputs like greater than 30 ....plz help!! The duplicate entries are stored in the right branch of the node
#include<stdio.h>
#include<time.h>
#include<stdlib.h>
typedef struct vertex{
int num;
struct vertex* r;
struct vertex* l;
} node;
void insert(node* T,int x)
{
if(x < T->num)
{
if(T->l == NULL)
{
T->l = (node*)malloc(sizeof(node));
T->l->num = x;
printf("%4d ",x);
return;
}
else
{
insert(T->l,x);
}
}
else if(x >= T->num)
{
if(x == T -> num)
if(T->r == NULL)
{
T->r = (node*)malloc(sizeof(node));
T->r->num = x;
printf("%4d ",x);
return;
}
else
insert(T->r,x);
}
}
main()
{
srand((unsigned int)time(NULL));
int i,n,m,x;
node* T;
printf("n = ");
scanf("%d",&n);
printf("\nm = ",&m);
scanf("%d",&m);
printf("\n\n\n+++ Inserting %d random integers between 1 and %d\n",n,m);
x = 1 + rand() % m;
T = (node*)malloc(sizeof(node));
T->num = x;
printf("%4d (1)",x);
for(i=1;i<n;i++)
{
x = 1+rand() % m;
insert(T,x);
if(i%8 == 7)
printf("\n");
}
printf("\n\n");
}

Answer 1

malloc() does not initialize memory, so set other member to NULL after allocation or use calloc(). Without this you will be accessing random memory when you do T->l or T->r.
T = malloc(sizeof(node));
T->num = x;
T->l = NULL;
T->r = NULL;
or
T = calloc(1, sizeof(node));
T->num = x;
Do this in all places where you use malloc()

Answer 2

malloc(noofbytes) function only allocate noofbytes space only does not initialize with NULL .
This is the problem with your code.
When you allocate memory
T->l = (node*)malloc(sizeof(node));
T->l->num = x;
you allocated memory of size of structure node but it is not initialized . Means
T->l->l and T->l->r is not NULL and have some garbage value.
when you traverse it T->l== NULL or T->r==NULL condition not get satisfied and so it gives segmentation fault.