For loop in C++ - Step-by-Step Execution

Concept Flow - For loop

Initialize i=0

↓

Check: i < 5?

No→EXIT

Yes↓

Execute body

↓

Update: i = i+1

↩Back to Check

The for loop starts by setting i to 0, then checks if i is less than 5. If yes, it runs the loop body, then increases i by 1 and repeats. If no, it stops.

Execution Sample

C++

for (int i = 0; i < 5; i++) {
    std::cout << i << std::endl;
}

Prints numbers from 0 to 4, one per line.

Execution Table

Iteration	i	Condition (i < 5)	Action	Output
1	0	true	Print 0, i++	0
2	1	true	Print 1, i++	1
3	2	true	Print 2, i++	2
4	3	true	Print 3, i++	3
5	4	true	Print 4, i++	4
6	5	false	Exit loop

💡 i reaches 5, condition 5 < 5 is false, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
i	0	1	2	3	4	5	5

Key Moments - 3 Insights

Why does the loop stop when i is 5 even though we print numbers starting from 0?

The loop condition checks if i < 5. When i becomes 5, this condition is false, so the loop stops before printing 5. See execution_table row 6.

When exactly does i increase in the loop?

i increases after the loop body runs, before the next condition check. This is shown in execution_table where 'i++' happens after printing.

What happens if we change i++ to i += 2?

i would increase by 2 each time, so the loop runs fewer times. The variable_tracker would show i values jumping by 2 instead of 1.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of i during the 3rd iteration?

A 1

B 3

C 2

D 0

💡 Hint

Check the 'i' column in the execution_table row labeled '3'

At which iteration does the loop condition become false?

A 5

B 6

C 4

D 1

💡 Hint

Look at the 'Condition (i < 5)' column in the execution_table where it is false

If we change i++ to i += 2, how would the variable_tracker change after the first iteration?

A i would be 2 instead of 1

B i would be 0 instead of 1

C i would be 3 instead of 1

D i would not change

💡 Hint

Refer to variable_tracker and think how i increments by 2 instead of 1

Concept Snapshot

for loop syntax: for (init; condition; update) { body }
Runs body while condition is true.
Init runs once at start.
Update runs after each body execution.
Stops when condition is false.

Full Transcript

A for loop in C++ starts by initializing a variable, here i=0. Then it checks if i is less than 5. If yes, it runs the loop body which prints i. After that, i increases by 1. This repeats until i reaches 5, when the condition becomes false and the loop stops. The variable i changes from 0 up to 5, but 5 is not printed because the loop stops before printing it.