Dynamically Creating a Singly Linked List in C - c

Question

I have a struct called employee in my program with the following definition:
struct employee {
int id;
int age;
struct *employee next;
};
How would I take in input from the user, create a struct from their input, and create a singly linked list using pointers? I'm having a lot of issues figuring out how to do this dynamically. In Java, this is easily done through the constructor but how would you do this in C?
EDIT: Assuming the input is simply two ints (id and age).

Answer 1

This is how you create a new employee struct. You are dynamically allocating the memory using malloc function.
struct employee *new_employee = (struct employee*)malloc(sizeof(struct employee));
Now, we need to fill the data into this newly created employee field:
new_employee -> id = input_id;
new_employee -> age = input_age;
As for the next pointer, it is usually given NULL value. This is to prevent the next pointer from pointing to any arbitrary memory location.
new_employee -> next = NULL;
Finally, we have to link the list. To do that, you have to point the next pointer of the previous employee field to the current employee field (ex:as you mentioned in comment, first one (9,3) having a next pointer to the second one (3, 2))
Since it is a singly linked list, we cannot backtrack. So, there are two methods to access the previous field.
First is to maintain a pointer that points to the last field of the link list.
Second is to traverse the entire list till the end, and when you reach the last element, change its next pointer.
Implementation of the second method:
node *temp = *start;
if(temp!=NULL)
{
while(temp -> next)
temp = temp -> next;
temp -> next = new_employee;
}
Hope it helps!

Answer 2

Note : don't give me fish teach me how to fish
This is an example :
struct node {
int value;
struct *node next;
};
How to create new Node pointer dynamically ?
node* aux = (node*) malloc(sizeof(node));
How to get user input ( safely ) ?
char line[256];
int i;
if (fgets(line, sizeof(line), stdin)) {
if (1 == sscanf(line, "%d", &i)) {
/* i can be safely used */
}
}
How to create a linked list's head ?
/* This will be the unchanging first node */
struct node *root;
/* Now root points to a node struct */
root = (struct node *) malloc( sizeof(struct node) );
/* The node root points to has its next pointer equal to a null pointer
set */
root->next = 0;
/* By using the -> operator, you can modify what the node,
a pointer, (root in this case) points to. */
root->value = 5;
How to add new node to the linked list ?
/* This won't change, or we would lose the list in memory */
struct node *root;
/* This will point to each node as it traverses the list */
struct node *conductor;
root = malloc( sizeof(struct node) );
root->next = 0;
root->value = 12;
conductor = root;
if ( conductor != 0 ) {
while ( conductor->next != 0)
{
conductor = conductor->next;
}
}
/* Creates a node at the end of the list */
conductor->next = malloc( sizeof(struct node) );
conductor = conductor->next;
if ( conductor == 0 )
{
printf( "Out of memory" );
return 0;
}
/* initialize the new memory */
conductor->next = 0;
conductor->value = 42;
Now you must be able to solve the problem easily .
Happy Coding :D