Get Length of Linked List in DSA C - Execution Trace

Concept Flow - Get Length of Linked List

Start at head node

↓

Is current node NULL?

Yes→Stop, length counted

No↓

Increment length count

↓

Move to next node

↩Back to check current node

Start from the head node, check if current node exists, count it, move to next, repeat until no more nodes.

Execution Sample

DSA C

int getLength(Node* head) {
    int length = 0;
    Node* current = head;
    while (current != NULL) {
        length++;
        current = current->next;
    }
    return length;
}

Counts nodes in a linked list by traversing from head to end.

Execution Table

Step	Operation	Current Node	Length Count	Pointer Changes	Visual State
1	Start at head	Node1	0	current = head	Node1 -> Node2 -> Node3 -> NULL
2	Check current != NULL	Node1	0	None	Node1 -> Node2 -> Node3 -> NULL
3	Increment length	Node1	1	None	Node1 -> Node2 -> Node3 -> NULL
4	Move to next node	Node2	1	current = current->next	Node1 -> Node2 -> Node3 -> NULL
5	Check current != NULL	Node2	1	None	Node1 -> Node2 -> Node3 -> NULL
6	Increment length	Node2	2	None	Node1 -> Node2 -> Node3 -> NULL
7	Move to next node	Node3	2	current = current->next	Node1 -> Node2 -> Node3 -> NULL
8	Check current != NULL	Node3	2	None	Node1 -> Node2 -> Node3 -> NULL
9	Increment length	Node3	3	None	Node1 -> Node2 -> Node3 -> NULL
10	Move to next node	NULL	3	current = current->next	Node1 -> Node2 -> Node3 -> NULL
11	Check current != NULL	NULL	3	None	Node1 -> Node2 -> Node3 -> NULL
12	Stop traversal	NULL	3	None	Final length = 3

💡 current becomes NULL at step 11, loop ends, length counted as 3

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
length	0	1	2	3	3
current	Node1	Node2	Node3	NULL	NULL

Key Moments - 3 Insights

Why do we check current != NULL before counting length?

Because if current is NULL, it means we reached the end of the list and there are no more nodes to count. See execution_table step 11 where current is NULL and loop stops.

Why do we move current to current->next after incrementing length?

We count the current node first, then move to the next node to continue counting. This order ensures no node is skipped. See execution_table steps 3 and 4.

What happens if the list is empty (head is NULL)?

The loop never runs because current starts as NULL. Length remains 0. This is shown by the loop condition failing immediately at step 2.

Visual Quiz - 3 Questions

Look at the execution_table, what is the length count at step 6?

A 1

B 2

C 3

D 0

💡 Hint

Check the 'Length Count' column at step 6 in the execution_table.

At which step does the current pointer become NULL?

A Step 9

B Step 11

C Step 10

D Step 12

💡 Hint

Look at the 'Current Node' column to see when it changes to NULL.

If the linked list had 5 nodes instead of 3, what would be the final length?

A 5

B 4

C 3

D 6

💡 Hint

Length equals the number of nodes counted, so final length matches node count.

Concept Snapshot

Get Length of Linked List:
- Start at head node
- While current node is not NULL:
  - Increment length
  - Move to next node
- Stop when current is NULL
- Return length counted

Full Transcript

To get the length of a linked list, start from the head node. Check if the current node exists. If yes, increase the length count by one. Then move to the next node. Repeat this until you reach a node that is NULL, which means the end of the list. The length count at this point is the total number of nodes in the list.