For loop in Rust - Step-by-Step Execution

Concept Flow - For loop

Start

↓

Get iterable

↓

Take next item?

No→Exit loop

Yes↓

Execute loop body

↓

Repeat: Take next item?

The for loop gets an iterable, takes each item one by one, runs the loop body, and stops when no items remain.

Execution Sample

Rust

fn main() {
    for i in 1..4 {
        println!("{}", i);
    }
}

This code prints numbers 1, 2, and 3 using a for loop over a range.

Execution Table

Iteration	i value	Condition (next item?)	Action	Output
1	1	Yes	Print 1	1
2	2	Yes	Print 2	2
3	3	Yes	Print 3	3
4	-	No	Exit loop	-

💡 No more items in range 1..4, loop ends

Variable Tracker

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

Key Moments - 2 Insights

Why does the loop stop after printing 3 and not include 4?

The range 1..4 in Rust includes 1, 2, and 3 but excludes 4, so the loop ends after 3 as shown in execution_table row 4.

What happens if the range is empty, like 5..5?

The loop never runs because there are no items to take, so the condition 'next item?' is No immediately, similar to execution_table row 4.

Visual Quiz - 3 Questions

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

A 1

B 3

C 2

D -

💡 Hint

Check the 'i value' column in execution_table row 2

At which iteration does the loop condition become false?

A Iteration 3

B Iteration 4

C Iteration 1

D Never

💡 Hint

Look at the 'Condition (next item?)' column in execution_table row 4

If the range changed to 1..3, how many times would the loop run?

A 2 times

B 1 time

C 3 times

D 0 times

💡 Hint

Ranges exclude the upper bound, so 1..3 includes 1 and 2 only, check variable_tracker for similar pattern

Concept Snapshot

Rust for loop syntax:
for variable in iterable {
    // code
}

Runs loop body once per item in iterable.
Ranges like 1..4 include start but exclude end.
Loop stops when no more items.

Full Transcript

This visual trace shows how a Rust for loop works by taking each item from an iterable one by one. The example uses a range 1..4 which includes 1, 2, and 3 but not 4. Each iteration assigns the current number to variable 'i' and prints it. The loop stops when there are no more items. The variable tracker shows how 'i' changes each iteration. Key moments clarify why 4 is excluded and what happens with empty ranges. The quiz tests understanding of iteration values and loop stopping conditions.