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 a variable, then checks a condition. If true, it runs the loop body, updates the variable, and repeats. If false, it stops.

Execution Sample

C

for (int i = 0; i < 5; i++) {
    printf("%d\n", i);
}

Prints numbers 0 to 4, one per line, using a for loop.

Execution Table

Iteration	i value	Condition (i < 5)	Action	Output
1	0	True	Print 0	0
2	1	True	Print 1	1
3	2	True	Print 2	2
4	3	True	Print 3	3
5	4	True	Print 4	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 equals 5?

Because the condition i < 5 becomes false at i = 5, so the loop exits as shown in execution_table row 6.

When is the variable i updated in the loop?

i is updated after the loop body executes, before the next condition check, as seen between each iteration in variable_tracker.

Does the loop body run when the condition is false?

No, the loop body only runs when the condition is true. When i = 5, condition is false, so the loop body does not run (execution_table row 6).

Visual Quiz - 3 Questions

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

A 3

B 1

C 2

D 4

💡 Hint

Check the 'i value' column in execution_table row 3.

At which iteration does the loop condition become false?

A 6

B 4

C 5

D 1

💡 Hint

Look at the 'Condition (i < 5)' column in execution_table row 6.

If we change the loop to i < 3, how many times will the loop run?

A 5 times

B 3 times

C 2 times

D 4 times

💡 Hint

Refer to the pattern in variable_tracker and execution_table for how condition controls iterations.

Concept Snapshot

for loop syntax in C:
for (initialization; condition; update) {
  // code to repeat
}

Loop runs while condition is true.
Variable updates after each iteration.
Stops when condition is false.

Full Transcript

A for loop in C starts by setting a variable, here i=0. It checks if i is less than 5. If yes, it runs the code inside the loop, printing i. Then it adds 1 to i. This repeats until i reaches 5, when the condition fails and the loop stops. The variable i changes from 0 up to 5, but the loop body runs only when i is 0 to 4. This is shown step-by-step in the execution table and variable tracker.