Can't find what's wrong with this simple C code

Question

Its a simple tree insertion and traversal code.

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

struct tree
{
    struct tree *left;
    struct tree *right;
    int value;
};

typedef struct tree node;

void insertNode(node **root, int val)
{
    node *temp = NULL;
    if(!(*root))
    {
        temp = (node*) malloc(sizeof(node));
        temp->value = val;
        temp->left = NULL;
        temp->right = NULL;
        *root = temp;
    }

    if(val < (*root)->value)
        insertNode(&(*root)->left, val);

    if(val >= (*root)->value)
        insertNode(&(*root)->right, val);
}

void preOrder(node *root)
{
    if(root)
    {   printf(" %d",root->value);
        preOrder(root->left);
        preOrder(root->right);
    }
}

void inOrder(node *root)
{
    if(root)
    {
        inOrder(root->left);
        printf(" %d",root->value);
        inOrder(root->right);
    }
}

void postOrder(node *root)
{
    if(root)
    {
        postOrder(root->left);
        postOrder(root->right);
        printf(" %d",root->value);
    }
}

void delTree(node *root)
{
    if(root)
    {
        delTree(root->left);
        delTree(root->right);
        free(root);
    }
}

int main()
{
    int val;
    char ch; ch = 'y';
    node *root;

    while(ch == 'y')
    {
        scanf("Enter the node value: %d", &val);
        insertNode(&root, val);
        scanf("Want to enter more: %c", &ch);
    }

    printf("\nInOrder traversal:\n");
    inOrder(root);
    printf("\nPreOrder traversal:\n");
    preOrder(root);
    printf("\nPostOrder traversal:\n");
    postOrder(root);

    delTree(root);
    printf("Tree Deleted.");

    return 0;
}

There seems to be no problem with the code and it shows no error. Though a warning is shown on compilation;

ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute

which seems to have initiated because of overlooking the return value of scanf, from ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]? .

But even on suppressing warning and compiling the executable file is not taking any input. Why is that. I am running the code on CodeBlocks IDE.

The case is same on ideone, http://ideone.com/jOnjEK .

Any help or suggestion is appreciated.

Also you need to initialize root in main() and in insertNode() you are inserting infinite copies of the same value recursively trough the right nodes. — Fernando, Jan 02 '15 at 18:17
@Chetan If you compile the code in C++, you *must* cast, in C you *should not* cast. [Do I cast the result of malloc?](http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) and [Should I explicitly cast malloc()'s return value?](http://stackoverflow.com/questions/953112/should-i-explicitly-cast-mallocs-return-value) — crashmstr, Jan 02 '15 at 18:38
@Chetan You have been harry to mark the best answer because your code contains other errors. — Vlad from Moscow, Jan 02 '15 at 18:54
@VladfromMoscow The code executed fine. Can you please tell me which errors, it might help — Chetan, Jan 02 '15 at 18:59
@Chetan Function insertNode has infinite recursion for the first NULL root. — Vlad from Moscow, Jan 02 '15 at 19:18

Gopi · Accepted Answer · 2015-01-02T18:19:08.590

1

scanf("Enter the node value: %d", &val); should be

scanf("%d", &val);

and

scanf("Want to enter more: %c", &ch); should be

scanf(" %c", &ch);

Assuming you are intending to this

printf("Enter the node value:\n");
if(scanf("%d", &val) != 1)
{
printf("Integer not read \n");
break;
} 

printf("Want to enter more:\n");
if(scanf(" %c", &ch) != 1)
{
printf("character not read\n");
break;
}

Make a note of the space before %c in the scanf()

edited Jan 02 '15 at 18:19

answered Jan 02 '15 at 18:12

Gopi

19,784
4
24
36

BTW, you should almost always test the result of `scanf` – Basile Starynkevitch Jan 02 '15 at 18:16
@Gopi Thanks a ton. Could you tell me why I have to use 'printf' instead of including sentence in 'scanf' – Chetan Jan 02 '15 at 18:32
Note: `scanf(" %c", &ch)` will only return `1` or `EOF`. Still like `if(scanf(" %c", &ch) != 1)`. – chux - Reinstate Monica Jan 02 '15 at 18:58

Can't find what's wrong with this simple C code

1 Answers1