While loop in C - Step-by-Step Execution

Concept Flow - While loop

Initialize variable

↓

Check condition

|Yes↓

Execute loop body

↓

Update variable

Back to Check↓

Exit loop

↩Back to Check

The while loop starts by checking a condition. If true, it runs the loop body and updates variables, then checks again. It stops when the condition is false.

Execution Sample

C

int i = 0;
while (i < 3) {
    printf("%d\n", i);
    i++;
}

Prints numbers 0, 1, 2 by repeating the loop while i is less than 3.

Execution Table

Step	i	Condition (i < 3)	Action	Output
1	0	True	Print 0, i = i + 1	0
2	1	True	Print 1, i = i + 1	1
3	2	True	Print 2, i = i + 1	2
4	3	False	Exit loop

💡 i reaches 3, condition i < 3 is False, loop stops

Variable Tracker

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

Key Moments - 2 Insights

Why does the loop stop when i is 3 even though the loop body is not executed?

Because the condition i < 3 is checked before the loop body each time (see execution_table step 4). When i is 3, the condition is false, so the loop exits immediately.

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

The condition i < 3 will always be true if i starts less than 3, causing an infinite loop. The execution_table shows i increasing each step to avoid this.

Visual Quiz - 3 Questions

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

A 3

B 2

C 1

D 0

💡 Hint

Check the 'i' column in execution_table row 3.

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

A Step 4

B Step 3

C Step 2

D Step 1

💡 Hint

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

If we remove 'i++' from the loop, what will happen?

A The loop will stop immediately

B The loop will print numbers 0 to 3

C The loop will run forever printing 0

D The program will crash

💡 Hint

Refer to key_moments about forgetting to update i causing infinite loop.

Concept Snapshot

while (condition) {
    // code to repeat
}

- Checks condition before each loop
- Runs code only if condition is true
- Updates inside loop needed to avoid infinite loops
- Stops when condition is false

Full Transcript

This example shows a while loop in C. We start with i = 0. The loop checks if i is less than 3. If yes, it prints i and adds 1 to i. This repeats until i reaches 3. When i is 3, the condition is false, so the loop stops. If we forget to increase i, the loop never ends because the condition stays true. The execution table shows each step with i's value, condition check, action, and output. This helps understand how the loop runs step-by-step.