While loop in Rust - 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, updates variables, then checks again. It stops when the condition is false.

Execution Sample

Rust

let mut count = 0;
while count < 3 {
    println!("Count is {}", count);
    count += 1;
}

This code prints the count from 0 to 2 using a while loop that runs while count is less than 3.

Execution Table

Step	count	Condition (count < 3)	Action	Output
1	0	true	Print and increment count to 1	Count is 0
2	1	true	Print and increment count to 2	Count is 1
3	2	true	Print and increment count to 3	Count is 2
4	3	false	Exit loop

💡 count reaches 3, condition 3 < 3 is false, loop stops

Variable Tracker

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

Key Moments - 2 Insights

Why does the loop stop when count is 3 even though the code increments count inside the loop?

The condition is checked before each loop iteration (see execution_table step 4). When count is 3, the condition count < 3 is false, so the loop exits before running the body again.

What happens if the condition is false at the start?

The loop body does not run at all. The condition is checked first (execution_table step 4 style), so if false initially, the loop exits immediately.

Visual Quiz - 3 Questions

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

A 1

B 0

C 2

D 3

💡 Hint

Check the 'count' 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 where it changes to false.

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

A 1 time

B 3 times

C 2 times

D 0 times

💡 Hint

Refer to variable_tracker and execution_table to see how condition affects loop count.

Concept Snapshot

while condition {
    // code to run
}

- Checks condition before each loop
- Runs body only if condition true
- Stops when condition false
- Useful for repeating until a condition changes

Full Transcript

This visual execution shows how a while loop works in Rust. We start with a variable count set to 0. The loop checks if count is less than 3. If yes, it prints the count and adds 1 to it. This repeats until count reaches 3. Then the condition is false and the loop stops. The variable tracker shows count changing from 0 to 3 step by step. Key moments explain why the loop stops when count is 3 and what happens if the condition is false initially. The quiz questions help check understanding of the loop steps and variable changes.