Linked lists with strings

Question

I'm trying to create a program that begins by parsing a number of strings and adding them into a Linked List, and then ending by printing out the occurrences of each string.

#include<stdio.h>
#include<stdlib.h>
#include<stdbool.h>
typedef struct Node Node;

struct Node
{
    char* word;
    int count;
    struct Node *next;
};

Node *head = NULL;
Node *curr = NULL;

Node* listAdd(char* word, bool toEnd) {
    Node* tmp = head;
    while (tmp) {
        if (strcmp(tmp, word) == 0) {
            tmp->count++;
            return tmp;
        }
        tmp = tmp->next;
    }
    printf("allocate memory for node");
    Node *ptr = malloc(sizeof(Node));

    printf("initialize count to 0");
    ptr->count = 0;

    printf("allocate memory to hold word");
    ptr->word = malloc(strlen(word) + 1);

    printf("copy the current word");
    strcpy(ptr->word, word);

    ptr->next = NULL;

    if (toEnd)
    {
        curr->next = ptr;
        curr = ptr;
    }
    else
    {
        ptr->next = head;
        head = ptr;
    }
    return ptr;
}

void printList()
{
    Node *ptr = head;
    while (ptr)
    {
        printf("\nThe word [%s] has had [%d] occurrences.\n",ptr->word, ptr->count);
        ptr = ptr->next;
    }
}

char* readWord()
{
    static char buffer[100];
    scanf("%s", buffer);
    printf("listAdd() call");
    listAdd(buffer);
    return buffer;
}

int main(void)
{
    int i = 0;
    printf("How many words would you like to type?\n");
    scanf("%d", &i);
    for (i; i != 0; i--)
    {
        readWord();
    }
    printList();
}

Current output:

How many words would you like to input?
3
hi
bye
yes
How many words would you like to input?
Occurrences: 12086064

Any assistance would be greatly appreciated — I'm still a novice at C coming from C# :(

Answer 1

Your code contains a couple of mistakes. First you are allocating your Node ptr twice:

Node* listAdd(char* word, bool toEnd) {
  // .. 

  Node *ptr = malloc(sizeof(Node));
  return ptr;
}

Remove the last one, right before the return statement.

You will also need to allocate memory to hold each read word. Right now you are overwriting the buffer each time you call readWord(). You would then do something like:

Node* listAdd(char* word, bool toEnd) {
  // allocate memory for node
  Node *ptr = malloc(sizeof(Node));
  // initialize count to 0
  ptr->count = 0;
  // allocate memory to hold word
  ptr->word = malloc(strlen(word) + 1);
  // copy the current word
  strcpy(ptr->word, word);

Your printList() function need look something like this:

void printList() {
  Node* ptr = head;
  while(ptr) {
    printf("Word: %s %d\n", ptr->word, ptr->count);
    ptr = ptr->next;
  }
}

Since you never check if the entered word already exists in your list each word will always be reported as having 1 occurance. This could be fixed like this:

// check if the word alreay exists in the list and then increment its count by 1
// this code should go at the top (before allocating ptr) in listAdd()
Node* tmp = head;
while(tmp) {
   if(strcmp(tmp->word, word) == 0) {
     tmp->count++;
     return tmp;
   }
   tmp = tmp->next;
}

Of course you should also free the allocated memory before exiting your application:

void freeList() {
  Node* ptr = head;
  Node* tmp = 0;
  while(ptr) {
    tmp = ptr->next;
    free(ptr->word);
    free(ptr);
    ptr = tmp;
  }

Answer 2

You need to use malloc and strcpy to store words, and strcmp to compare them. What you're doing is saving repeated references to the buffer array that you're reading the words into.