Nested loops in Go - Step-by-Step Execution

Concept Flow - Nested loops

Start outer loop i=0

↓

Start inner loop j=0

↓

Execute inner loop body

↓

Update inner loop j=j+1

↓

Check inner loop j < limit?

Yes→Repeat inner loop body

No↓

Update outer loop i=i+1

↓

Check outer loop i < limit?

Yes→Repeat inner loop

No↓

End

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

Go

for i := 0; i < 2; i++ {
    for j := 0; j < 3; j++ {
        fmt.Println(i, j)
    }
}

Print pairs of i and j where i goes 0 to 1 and j goes 0 to 2 for each i.

Execution Table

Step	i	j	Condition i<2	Condition j<3	Action	Output
1	0	0	true	true	Print (0,0)	(0 0)
2	0	1	true	true	Print (0,1)	(0 1)
3	0	2	true	true	Print (0,2)	(0 2)
4	0	3	true	false	Inner loop ends
5	1	0	true	true	Print (1,0)	(1 0)
6	1	1	true	true	Print (1,1)	(1 1)
7	1	2	true	true	Print (1,2)	(1 2)
8	1	3	true	false	Inner loop ends
9	2	0	false	true	Outer loop ends

💡 Outer loop i=2 fails condition i<2, so loops stop.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	After 7	After 8	Final
i	0	0	0	0	0	1	1	1	1	2
j	0	1	2	3	0	1	2	3	0	0

Key Moments - 3 Insights

Why does j reset to 0 after inner loop ends?

Because j is declared inside the inner loop, it starts fresh each time the inner loop begins (see rows 4 and 5 in execution_table).

Why does the outer loop increment only after inner loop finishes?

The outer loop waits for the inner loop to complete all its steps before increasing i (see transition from row 4 to 5).

What stops the loops from running forever?

The conditions i<2 and j<3 become false eventually, stopping loops (see rows 4 and 9 where conditions fail).

Visual Quiz - 3 Questions

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

A 2

B 1

C 0

D 3

💡 Hint

Check the 'j' column in row 6 of the execution_table.

At which step does the outer loop condition become false?

A Step 9

B Step 8

C Step 4

D Step 7

💡 Hint

Look at the 'Condition i<2' column and find where it is false.

If the inner loop condition changed to j<2, how many times would the inner loop print per outer loop iteration?

A 3 times

B 1 time

C 2 times

D 4 times

💡 Hint

Check how many times j runs from 0 while j<2 in the variable_tracker.

Concept Snapshot

Nested loops run one loop inside another.
Outer loop runs first.
Inner loop runs fully for each outer loop step.
Inner loop variable resets each time.
Loops stop when conditions fail.

Full Transcript

This example shows nested loops in Go. The outer loop variable i starts at 0 and runs while less than 2. For each i, the inner loop variable j runs from 0 to less than 3. Each pair (i,j) is printed. The inner loop finishes all its steps before the outer loop increments i. Variables i and j change as loops run. The loops stop when conditions become false. This helps understand how loops inside loops work step-by-step.