Do–while loop in C++ - Step-by-Step Execution

Concept Flow - Do–while loop

Start

↓

Execute body

↓

Check condition

Yes| No↓

Repeat

The do-while loop runs the code inside the loop first, then checks the condition. If true, it repeats; if false, it stops.

Execution Sample

C++

int i = 1;
do {
  cout << i << " ";
  i++;
} while (i <= 3);

Prints numbers 1 to 3 using a do-while loop that runs the body before checking the condition.

Execution Table

Step	i value	Condition (i <= 3)	Action	Output
1	1	true	Print 1, i = i + 1 (i=2)	1
2	2	true	Print 2, i = i + 1 (i=3)	2
3	3	true	Print 3, i = i + 1 (i=4)	3
4	4	false	Exit loop

💡 At step 4, i is 4, condition 4 <= 3 is false, so loop stops.

Variable Tracker

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

Key Moments - 3 Insights

Why does the loop body run even when the condition is false initially?

Because in a do-while loop, the body runs first before the condition is checked, as shown in step 1 of the execution_table.

When does the condition get checked in a do-while loop?

The condition is checked after the loop body runs, as seen after each action in the execution_table rows.

What happens when the condition becomes false?

The loop stops immediately after the condition check fails, as shown in step 4 where the condition is false and the loop exits.

Visual Quiz - 3 Questions

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

A 2

B 3

C 4

D 1

💡 Hint

Check the 'i value' column at step 3 in the execution_table.

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

A Step 2

B Step 3

C Step 4

D Step 1

💡 Hint

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

If the initial value of i was 5, how many times would the loop body run?

A 1 time

B 5 times

C 0 times

D Infinite times

💡 Hint

Remember do-while runs the body once before checking condition; see key_moments about initial run.

Concept Snapshot

do {
  // code to run
} while (condition);

- Runs loop body first, then checks condition.
- Repeats if condition true, stops if false.
- Executes at least once even if condition false initially.

Full Transcript

A do-while loop in C++ runs the code inside the loop first, then checks the condition. If the condition is true, it repeats the loop. If false, it stops. This means the loop body always runs at least once. For example, starting with i=1, the loop prints i and increases it by 1, then checks if i is less or equal to 3. It repeats until i becomes 4, then stops. This is different from a while loop that checks condition before running the body. The execution table shows each step with i's value, condition result, action taken, and output. The variable tracker shows how i changes after each iteration. Key moments clarify why the body runs first and when the loop stops. The quiz tests understanding of i's value at steps, when the loop ends, and behavior with different initial values.