list_delete_contains.c

// delete the first node from a linked list containing a value argument
// 25/5/2018
// Lyall Beveridge & Khye Ean Lowe

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

struct node {
    struct node *next;
    int          data;
};

struct node *delete_contains(int value, struct node *head);
struct node *strings_to_list(int len, char *strings[]);
void print_list(struct node *head);

// DO NOT CHANGE THIS MAIN FUNCTION

int main(int argc, char *argv[]) {
    if (argc < 2) {
        fprintf(stderr, "Usage: %s value list-elements\n", argv[0]);
        return 1;
    }
    int value = atoi(argv[1]);
    // create linked list from command line arguments
    struct node *head = strings_to_list(argc - 2, argv + 2);

    struct node *new_head = delete_contains(value, head);
    print_list(new_head);

    return 0;
}


// Delete the first node in the list containing the value `value`.
// The deleted node is freed.
// If no node contains `value`, the list is not changed.
// The head of the list is returned.

struct node *delete_contains(int value, struct node *head) {
    if (head == NULL) {
        return head;
    } else if (head->data == value) {
        struct node *after = head->next;
        free(head);
        if (after == NULL) {
            return NULL;
        } else {
            return after;
        }
    }

    struct node *current = head;
    struct node *previous = head;
    // break loop if the next value holds the correct data
    while (current->next != NULL && current->data != value) {
        previous = current;
        current = current->next;
    }

    // if loop was broken because there was the data in the next
    if (current->data == value) {

         // if the one after next is null, the current pointer will be the last
         if (current->next == NULL) {
             previous->next = NULL;
         } else {
             previous->next = current->next;
         }
         // in all cases the last value is not needed
         free(current);
    }


    return head;

}


// DO NOT CHANGE THIS FUNCTION
// create linked list from array of strings
struct node *strings_to_list(int len, char *strings[]) {
    struct node *head = NULL;
    for (int i = len - 1; i >= 0; i = i - 1) {
        struct node *n = malloc(sizeof (struct node));
        assert(n != NULL);
        n->next = head;
        n->data = atoi(strings[i]);
        head = n;
    }
    return head;
}

// DO NOT CHANGE THIS FUNCTION
// print linked list
void print_list(struct node *head) {
    printf("[");

    for (struct node *n = head; n != NULL; n = n->next) {
        // If you're getting an error here,
        // you have returned an invalid list
         printf("%d", n->data);
         if (n->next != NULL) {
            printf(", ");
        }
    }
    printf("]\n");
}