Error dereferencing pointer to incomplete type
in line: looptree cab = &firstNode; and subsequence use of the
pointer cab-> in function isThere.

What's wrong? Please help!
Thanks


#include <limits.h>
#include <stdlib.h>
#include <assert.h>

#define NUM_ELEMS 10000
#define TRUE 1
#define FALSE 0

typedef struct node *looptree;
typedef struct {
unsigned long long value;
looptree left;
looptree right;
}node;

int isThere(looptree cab, unsigned long long randomNumber);

int main () {

unsigned long long randomNumber; // 64 bits
randomNumber=123456789llu;

node firstNode;
looptree cab = &firstNode;
cab->left=NULL;
cab->right=NULL;
cab->value=randomNumber;

int counter = 0;
int foundLoop = FALSE;
while(!foundLoop){

randomNumber = randomNumber * randomNumber;
randomNumber = randomNumber / 100000llu;
randomNumber = randomNumber % 1000000000llu;

if (isThere(cab, randomNumber)){
printf("Loop at counter %d\n", counter);
foundLoop = TRUE;
}
printf("%llu\n", randomNumber);
counter++;
}

printf("\nFinish counter=%d\n", counter);
getchar();
return 0;
}

int isThere(looptree cab, unsigned long long key){
int isInTree = FALSE;
assert (cab !=NULL);

if (key == cab->value){
isInTree = TRUE;
} else if (key < cab->value){
if (cab->left == NULL){
cab->left = malloc(sizeof(node));
cab->left->value = key;
cab->left->left = NULL;
cab->left->right = NULL;
} else {
isInTree = isThere(cab->left, key);
}
}else {
if (cab->right == NULL){
cab->right = malloc(sizeof(node));
cab->right->value = key;
cab->right->left = NULL;
cab->right->right = NULL;
} else {
isInTree = isThere(cab->right, key);
}
}
return isInTree;
}

In an attempt to make sure that.. I don't exactly know what (you type less? your code is somehow clearer?) you've managed to produce a code piece which does not build. Does the idea of staying away from typedefs (at least at this point) look reasonable to you? Consider this:

but! You've cleverly made sure that there is no such thing as a "struct node", it's just "node", because of this:

There are also a number of other [unrelated] things which are wrong with your code.

noctilucent is correct (and fairly blunt) about it. Your use of multiple typedefs has resulted in incomplete types.
Consider the following:
This will let you use node to refer to a single node, with a complete type defined when you need it.

Hi and thank you! Actually I'm struggling with Tree structure in trying to insert a randomNumber if it's not in the tree yet going down left tree or the other.
Could you please point out my errs... "There are also a number of other [unrelated] things which are wrong with your code." I sure can use guidance from the experts.
Thanks again.... Oh by the way sorry I forgot to use indentation... Promise never to repeat this mistake.

You defined looptree as a pointer to a struct node and then you defined what a node is, but you haven't actually defined what a struct node is.

As a long time C++ programmer, my C is too rusty to be exactly sure what your code means, but I'm sure it isn't what you intended it too mean.

I'm not certain (too spoiled by the cleaner way structs work in C++) but maybe

First predeclare that struct node will be defined later, so you can correctly define a pointer to it.
Then define that pointer,
Then define both struct node and node (using looptree).

C++ corrects that particular language design flaw of C.

It doesn't look reasonable to me.
typedefs are great.

struct node_struct *left; from Matir's example is OK, but
looptree left; from the original example is nicer.

The trick is how to get that predeclare correct so looptree can be defined before the struct but as a pointer to it.

In an example this simple, Matir's approach looks better, because it avoids the need for any pre declaration. But in the real world of serious projects with pointers to structures, the circularities are not so easily suppressed. The forward declarations will be required and using typedefs (rather than things like struct node_struct * ) leads to more readable maintainable code.

I took a quick read through and didn't spot them.

The question wasn't addressed to you, so what is your point?

Once again: what's your point? Just a random piece of information? Look again, if you really care.

I think it is helpful to the OP to give an alternate opinion when I think the advice he already got was poor (just about avoiding typedef).

I don't normally comment on the impoliteness of other people providing answers in a technical forum. I have trouble myself in resolving the frequent conflict between helpful and polite. But I think you are being impolite in the course of being intentionally less helpful. What's your point?

I think I'll wait for the follow up question from the OP before trying that hard to spot the next bug.