While loops in MATLAB - Step-by-Step Execution

Concept Flow - While loops

Initialize variable

↓

Check condition

|Yes↓

Execute loop body

↓

Update variable

Back to Check↓

Exit loop

↩Back to Check

The loop starts by initializing a variable, then checks a condition. If true, it runs the loop body, updates the variable, and repeats. If false, it exits.

Execution Sample

MATLAB

count = 1;
while count <= 3
    disp(count);
    count = count + 1;
end

This code prints numbers 1 to 3 using a while loop that runs while count is less than or equal to 3.

Execution Table

Step	count	Condition (count <= 3)	Action	Output
1	1	true	disp(1); count = 2;	1
2	2	true	disp(2); count = 3;	2
3	3	true	disp(3); count = 4;	3
4	4	false	Exit loop

💡 count reaches 4, condition 4 <= 3 is false, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
count	1	2	3	4	4

Key Moments - 2 Insights

Why does the loop stop when count is 4 even though the loop body changes count?

The condition is checked before each loop iteration (see execution_table step 4). When count becomes 4, the condition count <= 3 is false, so the loop exits before running the body again.

What happens if we forget to update count inside the loop?

The condition will always be true (count stays 1), causing an infinite loop. The execution_table shows count increasing each step, which is necessary to eventually stop.

Visual Quiz - 3 Questions

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

A 2

B 3

C 4

D 1

💡 Hint

Check the 'count' column in execution_table row for step 3.

At which step does the condition become false and the loop stops?

A Step 3

B Step 2

C Step 4

D Step 1

💡 Hint

Look at the 'Condition' column in execution_table to find when it is false.

If we change the initial count to 4, what will happen to the loop execution?

A The loop will not run at all

B The loop will run once

C The loop will run infinitely

D The loop will run twice

💡 Hint

Refer to variable_tracker start value and condition check in execution_table step 1.

Concept Snapshot

while condition
    % code to repeat
    update variables
end

- The condition is checked before each loop run.
- Loop runs only if condition is true.
- Update variables inside to avoid infinite loops.

Full Transcript

This visual trace shows how a while loop works in MATLAB. We start with count = 1. The loop checks if count <= 3. Since it is true, it prints count and increases it by 1. This repeats until count becomes 4. At that point, the condition is false, so the loop stops. The variable tracker shows count changing from 1 to 4 step by step. Key points: the condition is checked before running the loop body, and updating the variable inside the loop is essential to avoid infinite loops.