Thread: Help with debugging my Linked List code.

I am having trouble getting my homework assignment to compile. There are about 10 errors that I cant seem to fix and I have been working for a while. I am not very good at programming so please bare with me!! But I appreciate all the help no matter what feedback you give! Thanks. Here we go:

Here is the sample input file and what the program is supposed to output:
Sample Input file:
7
6 0
0 5
5 1
3 0
2 6
4 3
5 3
4 1
6 1
3 5
1 3
6 2
5 2
5 3
1 3
5 2
0 0
3 1
6 4
6 5

Sample Output:

$ gcc hw2.c
$ ./a.out bad_input.txt
Unable to open file, enter a new file name: bad_input_2.txt
Unable to open file, enter a new file name: input.txt
Pre Sort
-
|0| 0 ->5 ->NULL = 5
-
-
|1| 3 ->3 ->NULL = 6
-
-
|2| 6 ->NULL = 6
-
-
|3| 1 ->5 ->0 ->NULL = 6
-
-
|4| 1 ->3 ->NULL = 4
-
-
|5| 2 ->3 ->2 ->3 ->1 ->NULL = 11
-
-
|6| 5 ->4 ->2 ->1 ->0 ->NULL = 12
-


Post Sort
-
|0| 1 ->3 ->NULL = 4
-
-
|1| 0 ->5 ->NULL = 5
-
-
|2| 3 ->3 ->NULL = 6
-
-
|3| 6 ->NULL = 6
-
-
|4| 1 ->5 ->0 ->NULL = 6
-
-
|5| 2 ->3 ->2 ->3 ->1 ->NULL = 11
-
-
|6| 5 ->4 ->2 ->1 ->0 ->NULL = 12



-------------------------------------------------------------------------

Here is my code that I have written so far. I commented what the functions are SUPPOSED to do. I have around 10 errors, most of them being pointer types( I SUCK at pointers).

Code:

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


#define MAX_FILE_LENGTH 20


typedef struct node_{
        int value;
/*1)    struct node_ next;*/
        struct node_* next;
}Node;


typedef Node* List;


int create_list(List**,FILE*);
void print_list(List*, int);
void free_list(List*, int);
int list_sum(Node*);
void insertion_sort(List*, int);
Node* new_node(int value);


/* Main will read in an input file from the command line, 
 * if the file fails to open the program should prompt the user for a new file, 
 * at no point should the program quit. If the program reads in a new file name, 
 * it can be up to size MAX_FILE_LENGTH. 
 * From there the program should read in the file, print it out, sort it, 
 * print it out again and then free it. */
int main (int argc, char* argv[]){


        if(argc != 2){
                printf("Incorrect number of command line arguments\n");
                return 1;
        }


        FILE* fp = fopen(argv[0], "r");


        while(fp == NULL){
                char file[MAX_FILE_LENGTH];
                printf("Unable to open file, enter a new file name: ");
                scanf("%d", file);
                fp = fopen(file, "r");
        }


        /*2)List array;*/
        List **array;
        int length = create_list(array, fp);


        printf("Pre Sort\n");
        print_list(array, length);


        insertion_sort(array,length);
        printf("\nPost Sort\n");
      print_list(array, length);


        return 0;
}


/*This function takes in a pointer to a list and a file pointer. 
 * The first line of the input file is the length of the array to be created.
 * Each subsequent line is composed of two numbers, an index and a value. 
 * The index is the index of the linked list where a node with the value of value should be inserted. 
 * So for example, if index = 0 and value = 3, and before the insertion array[0] = 1 -> 2 -> NULL, 
 * after the insertion array[0] = 3 -> 1 -> 2 -> NULL. This function returns the length of the array.*/
int create_list(List** array,FILE* fp){
        int length, i, index, value;


        fscanf(fp, "%d", &length);


        array = malloc(sizeof(Node));


        for(i = 0; i < length; i++)
                (*array)[i] = NULL;


        while(1){
                fscanf(fp, "%d %d", &index, &value);


                Node* node = new_node(value);


                node->next = array[index];


                array[index] = node;
        }


        return length;
}


/*Creates a new node of type Node, sets node->value = value and returns it. */
Node* new_node(int value){
        Node* node;
        node->value = value;
        node->next = NULL;


        return node;
}


/*Takes in the head to a single linked list and returns the sum of the values of each of its nodes. 
 * Ex: Node* head = 1 -> 2 -> 3 -> NULL then list_sum(head) = 6.*/
int list_sum(Node* head){


        return head->value + list_sum(head->next);
}


/*For each index in the array, print the index, the linked list it points to,
 * and the sum of its nodes. See the sample output for an example.*/
void print_list(List* array, int length){
        int i;


        for(i = 0; i < length; i++){
                Node *curr = array[i];


                printf(" -\n|%d| ", i);


                printf("%d ->", curr->value);


                curr = curr->next;


                printf("NULL = %d\n -\n", list_sum(array[i]));
        }


        /*3)return curr;*/
}


/*Sorts the array using insertion sort in ascending order by the sums of each linked list. */
void insertion_sort(List* array, int length){
        int* sum = malloc(sizeof(int) * length);
        int i, j, value;
        Node* node;


        for(i = 1; i < length; i++){
                value = sum[i];
                node = array[i];
                for(j = i; j > 0 && value < sum[j + 1]; j++)
                {
                        sum[j] = sum[j - 1];
                        array[j] = array[j - 1];
                }
        }


        printf("\n");
        free(sum);
}
/*Free all allocated memory.*/
/*4)void free_list(List array, int length){*/
void free_list(List* array, int length){
        int i;
        Node *curr;
        while(curr != NULL){
                Node* prev = curr;
                curr = curr->next;
                free(curr);
        }
}

here are the errors I am getting

homework2.c: In function ‘main’:
homework2.c:48: warning: passing argument 1 of ‘print_list’ from incompatible pointer type
homework2.c:15: note: expected ‘struct Node **’ but argument is of type ‘struct Node ***’
homework2.c:51: warning: passing argument 1 of ‘insertion_sort’ from incompatible pointer type
homework2.c:18: note: expected ‘struct Node **’ but argument is of type ‘struct Node ***’
homework2.c:53: warning: passing argument 1 of ‘print_list’ from incompatible pointer type
homework2.c:15: note: expected ‘struct Node **’ but argument is of type ‘struct Node ***’
homework2.c: In function ‘create_list’:
homework2.c:79: warning: assignment from incompatible pointer type
homework2.c:81: warning: assignment from incompatible pointer type

THANK YOU ALL I APPRECIATE THE HELP!!!

Originally Posted by nslice22

homework2.c:48: warning: passing argument 1 of ‘print_list’ from incompatible pointer type

Look at the function call:

Code:

print_list(array, length);

Look at the declaration of argument 1, i.e., array:

Code:

List **array;

Now look at the declaration of print_list:

Code:

void print_list(List* array, int length)

Clearly, there's a type mismatch: print_list expects a pointer to List as the first argument, but you passed a pointer to pointer to List.

I'd say the problem here is with the declaration of array. You should have written:

Code:

List *array;

This would immediately fix the type mismatch here, but of course you would then have a problem here:

Code:

int length = create_list(array, fp);

My initial inclination is that you should change it to:

Code:

int length = create_list(&array, fp);

However, on further investigation, you seem to have more levels of indirection than is desirable. I spotted:

Code:

typedef Node* List;

This can work, but it is problematic because the typedef hides the fact that List is actually a pointer. I would prefer:

Code:

typedef struct {
    Node *head;
} List;

But if you have to have this typedef, then you have a problem in that even if you declare array in main to be:

Code:

List *array;

You need to allocate space for what array points to, and then allocate space for what the pointer that array points to points to. If you take my suggested definition of List as a struct instead, then you can declare array as:

Code:

List array;

and then pass it to create_list:

Code:

int length = create_list(&array, fp);