Loop execution flow in Rust - Step-by-Step Execution

Concept Flow - Loop execution flow

Initialize counter i=0

↓

Check condition i < 3?

No→EXIT LOOP

Yes↓

Execute loop body

↓

Update counter i = i + 1

↩Back to condition check

The loop starts by setting a counter, checks if it meets the condition, runs the loop body if yes, updates the counter, and repeats until the condition is false.

Execution Sample

Rust

fn main() {
    let mut i = 0;
    while i < 3 {
        println!("i = {}", i);
        i += 1;
    }
}

This Rust code runs a loop printing the value of i from 0 to 2.

Execution Table

Step	i value	Condition i < 3?	Action	Output
1	0	true	Print i, i = 0; i = i + 1	i = 0
2	1	true	Print i, i = 1; i = i + 1	i = 1
3	2	true	Print i, i = 2; i = i + 1	i = 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 equals 3?

Because the condition i < 3 becomes false at step 4 in the execution_table, so the loop exits.

When is the value of i increased during the loop?

After printing i in each iteration, i is increased by 1 as shown in the Action column of steps 1 to 3.

Visual Quiz - 3 Questions

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

A 2

B 0

C 1

D 3

💡 Hint

Check the 'i value' column at step 2 in the execution_table.

At which step does the loop condition become false?

A Step 4

B Step 3

C Step 1

D Step 2

💡 Hint

Look at the 'Condition i < 3?' column in the execution_table.

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

A 3 times

B 2 times

C 1 time

D 0 times

💡 Hint

Refer to the variable_tracker and how the condition controls loop iterations.

Concept Snapshot

Rust loop execution flow:
- Initialize counter before loop
- Check condition before each iteration
- Run loop body if condition true
- Update counter inside loop
- Repeat until condition false
- Loop exits cleanly

Full Transcript

This example shows a Rust while loop starting with i = 0. Each step checks if i is less than 3. If yes, it prints i and increases i by 1. When i reaches 3, the condition fails and the loop stops. The variable i changes from 0 to 3 over the loop. Key points are when the condition is checked and when i is updated. The loop runs exactly 3 times, printing i values 0, 1, and 2.