linkedlist.c

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

typedef struct node {
  int val;
  struct node *next;
} node_t;

// pop will return the element that is popped and moves the head
// to the next head
int pop(node_t ** head) {
  int retval = -1;
  node_t * next_node = NULL;
  if (*head == NULL) {
    return -1;
  }

  next_node = (*head)->next;
  retval = (*head)->val;
  free(*head);
  *head = next_node;

  return retval;
}

int remove_by_value(node_t ** head, int val) {
  node_t *previous, *current;

  if (*head == NULL) {
    return -1;
  }

  if ((*head)->val == val) {
    return pop(head);
  }
  previous = current = (*head)->next;
  while(current) {
    if (current->val == val) {
      previous->next = current->next;
      free(current);
      return val;
    }
    previous = current;
    current = current->next;
  }
  return -1;
}


void print_list(node_t *head) {
  node_t *current = head;

  while (current != NULL) {
    printf("%d\n", current->val);
    current = current->next;
  }
}

int main() {
  node_t * test_list = malloc(sizeof(node_t));
  test_list->val = 1;
  test_list->next = malloc(sizeof(node_t));
  test_list->next->val = 2;
  test_list->next->next= NULL;
  printf("Printing the linked list\n");
  print_list(test_list);
  remove_by_value(&test_list, 1);
  printf("Printing the linked list again\n");
  print_list(test_list);
}