C program compiles but won't print out the test cases in the main method

Question

The whole point of my C code is to insert string nodes in alphabetical order. Here is my code....

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


typedef struct node {
    char * word;
    struct node * left;
    struct node * right;
}treeNode;

treeNode * head = NULL;

void traverse (treeNode * h)
{
    if(h->left == NULL){
        scanf("%s ", h->word);
        if(h->right != NULL){
            traverse(h->right);
        }
    }
    else{
        traverse(h->left);
        printf("%s ", h->word);
        if(h->right != NULL){
            traverse(h->right);
        }
    }

    treeNode *newNode(char * s)
    {
        treeNode *insert = (treeNode*)malloc(100*sizeof(treeNode));
        insert->left = NULL;
        insert->right = NULL;
        insert->word = s;
        return insert;
    }

    treeNode * addNode (treeNode * h, char * s)
    {
        if(h == NULL){
            return newNode(s);
        }
        else{
            if (strcmp (h->word, s)> 0){
                h->left = addNode(h->left,s);
            }
            else{
                h->right = addNode(h->right,s);
            }
        }
        return h;
    }
    void main()
    {

        printf("\nTest Animals 1");
        head = insert(head, "dog");
        insert(head, "horse");
        insert(head, "frog");
        insert(head, "fish");
        insert(head, "cow");
        traverse(head);
        head = NULL;

        printf("\nTest Food 2");
        head = insert(head, "pizza");
        insert(head, "sushi");
        insert(head, "burger");
        insert(head, "salad");
        insert(head, "nuggets");
        traverse(head);
        head = NULL;

        printf("\nTest Sports 3");
        head = insert(head, "soccer");
        insert(head, "basketball");
        insert(head, "football");
        insert(head, "tennis");
        insert(head, "gymnastics");
        traverse(head);
        head = NULL;

    }

It compiles perfectly with no errors at all but my main method isn't allowing me to print out my sample test cases. Could it be a problem in the code itself? I've looked it all over and I do not see what is wrong with it. This is also my first C code so I apologize if there are mistakes that I may have missed.

Welcome to SO! Can you explain why you're using `scanf` and `printf` in your traversal? What sort of output are you expecting? `(treeNode*)malloc(100*sizeof(treeNode))` doesn't need a cast and `100` seems arbitrary. I can't find your `insert` method and `addNode` is never used. — ggorlen, Nov 01 '18 at 01:59
"It compiles perfectly with no errors at all" It most certainly does not! bad.c:31:3: error: function definition is not allowed here bad.c:40:1: error: function definition is not allowed here bad.c:55:1: error: function definition is not allowed here bad.c:86:2: error: expected '}' — Joseph Sible-Reinstate Monica, Nov 01 '18 at 02:01
Hello! A lot of these methods I looked up online as I was creating my code, scanf should not be there. Basically though, I was trying to put my nodes list in alphabetical order. — Ashford13in, Nov 01 '18 at 02:01
The function `insert` is not declared/defined in your code. Also, to allocate a node you just need `treeNode *insert = malloc(sizeof(treeNode));`, don't multiply by 100 — Barmak Shemirani, Nov 01 '18 at 02:04
Oh, I see the problem now, I'm just not sure what parameters I should use when calling the addNode method in my main function. Still struggling — Ashford13in, Nov 01 '18 at 02:04
It looks like you're missing the `}` at the end of `traverse`, so all the other functions are defined internally to it. — Barmar, Nov 01 '18 at 02:05
How do I go about declaring the insert method? I thought that I had already done that in my newNode() method — Ashford13in, Nov 01 '18 at 02:07

Barmak Shemirani · Accepted Answer · 2018-11-06T07:47:29.750

treeNode *newNode(char * s)
{
    treeNode *insert = (treeNode*)malloc(100*sizeof(treeNode));
    insert->left = NULL;
    insert->right = NULL;
    insert->word = s;
    return insert;
}

Use malloc(sizeof(treeNode)) to allocate a single node. Don't multiply by 100 unless you want memory for 100 nodes.

Don't just assign pointers to literal strings (insert->word = s) Instead, allocate memory for that string, and use strcpy. Example:

insert->word = malloc(strlen(str) + 1);
strcpy(insert->word, str);

If the goal is to insert items sorted, then you have to walk through all items. I recommend avoiding recursive functions, specially for beginners.

Lastly, compile your program with maximum warnings. Address all of the warnings.

typedef struct node {
    char * word;
    struct node * left;
    struct node * right;
}treeNode;

void traverse(treeNode *head)
{
    treeNode *ptr = head;
    while(ptr)
    {
        printf("%s, ", ptr->word);
        ptr = ptr->right;
    }
    printf("\n");
}

treeNode *insert(treeNode *head, char *str)
{
    treeNode *ptr = malloc(sizeof(treeNode));
    ptr->left = NULL;
    ptr->right = NULL;
    ptr->word = malloc(strlen(str) + 1);
    strcpy(ptr->word, str);

    if(head == NULL)
    {
        head = ptr;
        return head;
    }
    else
    {
        int inserted = 0;
        treeNode *walk = head;
        treeNode *prev = NULL;
        while(walk)
        {
            if(strcmp(ptr->word, walk->word) < 0)
            {
                if(walk == head)
                {
                    ptr->right = head;
                    head = ptr;
                }
                else
                {
                    prev->right = ptr;
                    ptr->right = walk;
                }
                inserted = 1;
                break;
            }
            prev = walk;
            walk = walk->right;
        }

        if(!inserted)
        {
            prev->right = ptr;
        }
    }

    return NULL;
}

int main(void)
{
    treeNode *head = NULL;
    printf("\nTest Animals 1");
    head = insert(head, "dog");
    insert(head, "horse");
    insert(head, "frog");
    insert(head, "fish");
    insert(head, "cow");
    traverse(head);
    return 0;
}

If that's meant to be a binary search tree then follow the code below:

void traverse(treeNode *head)
{
    if(head)
    {
        traverse(head->left);
        printf("%s \n", head->word);
        traverse(head->right);
    }
}

treeNode *insert(treeNode *head, char * s)
{
    if(head == NULL)
    {
        treeNode *ptr = malloc(sizeof(treeNode));
        ptr->left = NULL;
        ptr->right = NULL;
        ptr->word = malloc(strlen(s) + 1);
        strcpy(ptr->word, s);
        return ptr;
    }

    if(strcmp(head->word, s) > 0)
        head->left = insert(head->left, s);
    else 
        head->right = insert(head->right, s);

    return head;
}

void main(void)
{
    treeNode *head = NULL;
    head = insert(NULL, "dog");
    insert(head, "horse");
    insert(head, "frog");
    insert(head, "fish");
    insert(head, "cow");
    traverse(head);
    return 0;
}

C program compiles but won't print out the test cases in the main method

1 Answers1