Search for a Value in Linked List in DSA C - Execution Trace

Concept Flow - Search for a Value in Linked List

Start at head node

↓

Check if current node is NULL?

Yes→Value not found, stop

No↓

Compare current node value with target

↓

Found value, stop

↩Back to check NULL

Start from the head node, check each node's value. If it matches the target, stop. Otherwise, move to the next node until the list ends.

Execution Sample

DSA C

Node* current = head;
while (current != NULL) {
  if (current->value == target) {
    return current;
  }
  current = current->next;
}
return NULL;

This code searches each node in the linked list for the target value and returns the node if found, else NULL.

Execution Table

Step	Operation	Current Node Value	Pointer Changes	Visual State
1	Start at head	3	current = head (3)	[3] -> [5] -> [7] -> NULL
2	Compare current value with target (5)	3	No pointer change	[3] -> [5] -> [7] -> NULL
3	Move to next node	5	current = current->next (5)	[3] -> [5] -> [7] -> NULL
4	Compare current value with target (5)	5	No pointer change	[3] -> [5] -> [7] -> NULL
5	Value matches target	5	Stop search	[3] -> [5] -> [7] -> NULL

💡 Value 5 found at step 5, search stops.

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 5
current	head (3)	3	5	5
target	5	5	5	5

Key Moments - 3 Insights

Why do we check if current is NULL before comparing values?

Because if current is NULL, it means we've reached the end of the list without finding the value. Checking NULL first prevents errors when accessing current->value. See execution_table step 2.

What happens if the value is not in the list?

The loop continues moving current to next nodes until current becomes NULL, then the search stops returning NULL. This is shown by the exit condition in the concept flow.

Why do we move current to current->next after each failed comparison?

To check the next node in the list. Without moving forward, the search would get stuck on the same node. See execution_table step 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of current after step 3?

A 3

B 7

C 5

D NULL

💡 Hint

Check the 'Pointer Changes' and 'Current Node Value' columns at step 3.

At which step does the search stop because the value is found?

A Step 3

B Step 5

C Step 4

D Step 2

💡 Hint

Look for the row where 'Value matches target' and 'Stop search' appear.

If the target was 7 instead of 5, at which step would the value be found?

A Step 6

B Step 3

C Step 5

D Step 4

💡 Hint

Think about how many nodes are checked before finding 7 in the list.

Concept Snapshot

Search in Linked List:
- Start at head node
- While current != NULL:
  - Check if current->value == target
  - If yes, stop and return node
  - Else move to current->next
- If end reached (NULL), value not found

Full Transcript

This visualization shows how to search for a value in a linked list. We start at the head node and check if the current node's value matches the target. If it does, we stop and return the node. If not, we move to the next node and repeat. If we reach the end of the list (NULL) without finding the value, the search ends with no result. The execution table tracks each step, showing the current node's value, pointer changes, and the list's visual state. Key moments clarify why we check for NULL first, what happens if the value is missing, and why we move forward in the list. The quiz tests understanding of pointer positions and stopping conditions.