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

Concept Flow - While loop

Initialize variable

↓

Check condition

↓

Execute loop body

↓

Update variable

↩Back to Check condition

The while loop checks a condition before each iteration. If true, it runs the loop body and updates variables, then checks again. If false, it exits.

Execution Sample

C++

#include <iostream>
using namespace std;

int main() {
    int i = 0;
    while (i < 3) {
        cout << i << " ";
        i++;
    }
    return 0;
}

This code prints numbers 0, 1, 2 by looping while i is less than 3.

Execution Table

Step	i value	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 3 < 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 equals 3?

Because the condition i < 3 becomes false at step 4 (see execution_table row 4), so the loop exits.

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

The condition i < 3 would always be true, causing an infinite loop because i never changes (no progress).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of i at step 2?

A 0

B 2

C 1

D 3

💡 Hint

Check the 'i value' column in execution_table row 2.

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

A Step 3

B Step 4

C Step 2

D Step 1

💡 Hint

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

If we change the condition to i < 2, how many times will the loop run?

A 2 times

B 1 time

C 3 times

D 0 times

💡 Hint

Check variable_tracker and think when i reaches 2, condition i < 2 becomes false.

Concept Snapshot

while (condition) {
    // code to repeat
    // update variables
}

- Checks condition before each loop
- Runs body only if condition true
- Updates variables inside to avoid infinite loop
- Stops when condition is false

Full Transcript

A while loop starts by checking a condition. If the condition is true, it runs the code inside the loop body. Then it updates variables, usually to move toward stopping the loop. It repeats this check and run cycle until the condition becomes false, then it exits. For example, starting with i = 0, while i is less than 3, it prints i and increases i by 1. When i reaches 3, the condition fails and the loop stops. Forgetting to update i causes an infinite loop because the condition never becomes false.