Segmentation error in C [closed] - c

Question

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Closed 10 years ago.
EDIT: the default for the switch is "invalid option", and i am just trying to create a tree that's all, the program is getting compiled and when i select the option for creating a tree it simply says segmentation error
I've been doing simple data structures programs for the past few days, and the segmentation error is the one bothering me a lot, i researched on the internet about the error and got this link and actually it didn't help.
I'm trying to create a binary search tree. and the return type for create is not void, it struct tree *
program:
struct tree{
int data;
struct tree *rchild, *lchild;
};
struct tree * create(struct tree * root, int d){
if(root==NULL) {
root = (struct tree *) malloc(sizeof(struct tree));
root->data=d;
root->rchild=NULL;
root->lchild=NULL;
}else if(root->data < d) create(root->rchild, d);
else if(root->data > d) create(root->lchild, d);
else if(root->data == d) printf("duplication error");
}
main(){
struct tree *root;
int choice, c;
while(choice!=5){
printf("Enter choice\n1-insert into tree\n5-exit");
scanf("%d", &choice);
switch(choice){
case 1:
printf("enter data to be inserted");
scanf("%d",&c);
printf("error after scanf ");
create(root,c);
break;
case 5: exit(0); default: printf("invalid option");
}
}
}
and the OS i'm using is Backtrack 5 R1
to the one who gave -1: Sir, please tell the answer to my question if it's so silly and non constructive
there is a similar linked list question, I've also answered that question, and I'm writing a tree program by the way.

Answer 1

At least, I do not think the create() can work correctly.
You should use struct tree ** instead of struct tree *.
As your node root is NULL, create(root) means create(NULL), which can not assign the allocated memory to root. You should define it as create(struct tree**), and call it with create(&root)

Answer 2

You are malloc'ing root in the create function, but there is no reason why that survives the call, since it is not being passed by reference. If you passed &root, you could then change *root. As it is, you do not create new nodes in your tree... every time you return from create, the root pointer is NULL...
Alternatively, you could return the new value of root as the return value of the call, and call it with
root = create( root, c);
You can prove this to yourself by adding
printf("root is now %p\n", root);
after your create call...
In short, the following works:
struct tree{
int data;
struct tree *rchild, *lchild;
};
struct tree* create(struct tree * root, int d){
printf("creating node with d = %d\n", d);
if(root==NULL) {
root = (struct tree *) malloc(sizeof(struct tree));
root->data=d;
root->rchild=NULL;
root->lchild=NULL;
}else if(root->data < d) create(root->rchild, d);
else if(root->data > d) create(root->lchild, d);
else if(root->data == d) printf("duplication error");
return root;
}
main(){
struct tree *root;
int choice, c;
while(choice!=5){
printf("Enter choice\n1-insert into tree\n5-exit");
scanf("%d", &choice);
printf("root is now %p\n", root);
switch(choice){
case 1:
printf("enter data to be inserted");
scanf("%d",&c);
printf("made it past scanf\n");
root = create(root,c);
break;
case 5: exit(0);
default: printf("invalid option\n");
}
}
}