Unable to perfrom inorder traversal in a binary tree in C

**Pingu** · 01-16-2014

Following is the code for inserting elements in a tree and then retrieving them back using inorder traversal technique.......
elements are getting inserted just fine,but the code doesn't displays the elements of the tree while performing inorder traversal...

Code:

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


struct node{
   int data;
   struct node *right;
   struct node *left;
   }*z,*t,*root=NULL,*x=NULL,*y=NULL;


void inorder_visit(struct node *temp);//function to traverse tree with inorder technique


void insert_node(struct node *temp,struct node *z);//function to insert elements in a tree


int main(){
int n,i;
for(i=0;i<5;++i){
printf("enter the data:");
scanf("%d",&n);


z=(struct node*)malloc(sizeof(int));


if(z==NULL)
    printf("sorry!");
else{
    z->data=n;
    z->left=NULL;
    z->right=NULL;




    t=root;
    insert_node(t,z);
    }
}


t=root;
inorder_visit(t);




return 0;
}


void inorder_visit(struct node *temp){
if(temp!=NULL){
inorder_visit(temp->left);
printf("%d\t",temp->data);
inorder_visit(temp->right);
}
}


void insert_node(struct node *temp,struct node *z){
    if(temp==NULL)
        temp=z;
    else {
            if(z->data<=temp->data)
        insert_node(temp->left,z);
    else
        insert_node(temp->right,z);}
}

**hk_mp5kpdw** · 01-16-2014

elements are getting inserted just fine

Are you sure?

Code:

z=(struct node*)malloc(sizeof(int));

Your size is wrong here. You should also avoid casting malloc in C.

Code:

t=root;

This simply sets t to NULL all the time destroying whatever it may have been pointing at. You probably shouldn't be using the variable t at all. I'd stick to just using your root variable in place of t.

Code:

void insert_node(struct node *temp,struct node *z);

...

insert_node(t,z);

Like any function in C meant to alter the value of the variable passed into it (and have the changed value persist after the function call), you must pass in a pointer to what you need changed... even if what you are passing in is already in effect a pointer. You are essentially trying to change root (forget about t here). If you expect the value of the pointer root to be altered by the call to insert_node, then that pointer must be passed by pointer. This means that this parameter must be a pointer to a pointer (double pointer).

There is a way around this by having the function return the pointer passed in which you then immediately reassign to itself so that the call (in main at least) would look like this:

Code:

root = insert_node(root,z);

...you'd still need to make similar changes to the recursive calls.

Making the above/below changes I was able to get the code to compile and run and print the list (inorder) without issues:

Correct size parameter for the malloc call
Get rid of variable t, use root in its place
Make insert_node take a pointer to a pointer for the first argument (along with other associated changes needed by this alteration)

**iMalc** · 01-17-2014

Yeah you got it back-to-front.
The in-order traversal code is exactly right but the insertion is quite wrong.

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