Nested loops in MATLAB - Step-by-Step Execution

Concept Flow - Nested loops

Start Outer Loop i=1

↓

Start Inner Loop j=1

↓

Execute Inner Loop Body

↓

Update j = j+1

↓

Check j <= max_j?

No→End Inner Loop

Yes↓

Update i = i+1

↓

Check i <= max_i?

No→End Outer Loop

↩Back to Inner Loop Body

The outer loop runs first. For each outer loop step, the inner loop runs completely. Then the outer loop moves to the next step.

Execution Sample

MATLAB

for i = 1:2
    for j = 1:3
        disp([i, j])
    end
end

Print pairs of i and j where i goes 1 to 2 and j goes 1 to 3 for each i.

Execution Table

Step	i	j	Condition i<=2	Condition j<=3	Action	Output
1	1	1	True	True	Print [1 1]	[1 1]
2	1	2	True	True	Print [1 2]	[1 2]
3	1	3	True	True	Print [1 3]	[1 3]
4	1	4	True	False	Exit inner loop
5	2	1	True	True	Print [2 1]	[2 1]
6	2	2	True	True	Print [2 2]	[2 2]
7	2	3	True	True	Print [2 3]	[2 3]
8	2	4	True	False	Exit inner loop
9	3	1	False	True	Exit outer loop

💡 i reaches 3, condition i<=2 is False, so outer loop ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	After 7	After 8	Final
i	1	1	1	1	2	2	2	2	3	3
j	1	2	3	4	1	2	3	4	1	1

Key Moments - 3 Insights

Why does the inner loop restart j from 1 for each new i?

Because the inner loop is inside the outer loop, it runs fully for each i. See execution_table rows 1-4 for i=1 and rows 5-8 for i=2, where j resets to 1 each time.

When does the outer loop variable i increase?

After the inner loop finishes all its iterations. Look at execution_table row 4 where j=4 ends inner loop, then i increments from 1 to 2 at row 5.

Why does the loop stop at i=3?

Because the outer loop condition i<=2 becomes false at i=3, stopping the loop. See execution_table row 9 where condition i<=2 is False.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of j at step 6?

A 2

B 3

C 1

D 4

💡 Hint

Check the 'j' column in execution_table row 6.

At which step does the inner loop end for i=1?

A Step 3

B Step 4

C Step 5

D Step 9

💡 Hint

Look for when 'Condition j<=3' becomes False for i=1 in execution_table.

If the outer loop changed to i=1:3, how many total print outputs would there be?

A 6

B 9

C 12

D 3

💡 Hint

Multiply outer loop count (3) by inner loop count (3) to find total prints.

Concept Snapshot

Nested loops run one loop inside another.
Outer loop runs first.
For each outer step, inner loop runs fully.
Use nested for loops in MATLAB like:
for i=1:n
  for j=1:m
    % code
  end
end
Inner loop resets each outer iteration.

Full Transcript

Nested loops in MATLAB mean one loop runs inside another. The outer loop variable i starts at 1 and goes to 2. For each i, the inner loop variable j runs from 1 to 3. Each pair (i,j) is printed. The inner loop finishes all j values before i increases. When i reaches 3, the outer loop stops because the condition i<=2 is false. Variables i and j change as the loops run. The inner loop resets j to 1 for each new i. This pattern lets you do repeated tasks in a grid or matrix style.