Loop execution flow in Rust

Introduction

Loops help repeat actions many times without writing the same code again and again.

When you want to count from 1 to 10 and do something each time.

When you need to check every item in a list or collection.

When you want to keep asking a user for input until they give a valid answer.

When you want to repeat a task until a certain condition is met.

Syntax

Rust

loop {
    // code to repeat
    if condition {
        break;
    }
}

loop creates an infinite loop unless you use break to stop it.

You can use continue to skip the rest of the current loop and start the next cycle.

Examples

This loop counts from 1 to 5 and then stops using break.

Rust

let mut count = 0;
loop {
    count += 1;
    println!("Count is {}", count);
    if count == 5 {
        break;
    }
}

This loop prints only odd numbers from 1 to 11 by skipping even numbers with continue.

Rust

let mut n = 0;
loop {
    n += 1;
    if n % 2 == 0 {
        continue; // skip even numbers
    }
    println!("Odd number: {}", n);
    if n > 10 {
        break;
    }
}

Sample Program

This program runs a loop that prints the current iteration number. When it reaches 3, it prints a message and stops the loop.

Rust

fn main() {
    let mut i = 1;
    loop {
        println!("Loop iteration: {}", i);
        if i == 3 {
            println!("Reached 3, stopping loop.");
            break;
        }
        i += 1;
    }
}

Important Notes

Use break to stop a loop when you want to exit early.

Use continue to skip the rest of the current loop cycle and start the next one.

Infinite loops can crash your program if you forget to use break.

Summary

Loops repeat code until you tell them to stop.

break stops the loop completely.

continue skips to the next loop cycle.

Practice

1. What does the break statement do inside a Rust loop?

easy

A. It restarts the loop from the beginning.

B. It skips the current iteration and continues with the next one.

C. It pauses the loop until a condition is met.

D. It stops the loop immediately and exits it.

Solution

1. Step 1: Understand the role of break in loops

   The break statement immediately stops the loop and exits it.

2. Step 2: Compare with other loop controls

   continue skips to the next iteration, but break ends the loop entirely.

3. Final Answer:

   It stops the loop immediately and exits it. -> Option D

4. Quick Check:

   break stops loop = C [OK]

Hint: Remember: break = stop loop, continue = skip iteration [OK]

Common Mistakes:

• Confusing break with continue
• Thinking break pauses instead of stops
• Assuming break restarts the loop

2. Which of the following is the correct syntax to skip the current iteration in a Rust for loop?

easy

A. skip;

B. continue;

C. break;

D. next;

Solution

1. Step 1: Identify the keyword to skip iteration

   In Rust, continue; skips the rest of the current loop iteration and moves to the next.

2. Step 2: Check other options for correctness

   break; stops the loop, skip; and next; are not valid Rust keywords for this purpose.

3. Final Answer:

   continue; -> Option B

4. Quick Check:

   Skip iteration = continue [OK]

Hint: Use continue to skip current loop iteration [OK]

Common Mistakes:

• Using break instead of continue
• Using non-existent keywords like skip or next
• Omitting the semicolon

3. What will be the output of this Rust code?

let mut count = 0;
loop {
    count += 1;
    if count == 3 {
        break;
    }
    println!("{}", count);
}

medium

A. 1 2 3

B. 0 1 2

C. 1 2

D. 3

Solution

1. Step 1: Trace the loop iterations and print statements

   Loop increments count from 0 to 1, prints 1; then 2, prints 2; when count is 3, break stops loop before printing.

2. Step 2: Determine printed values

   Only 1 and 2 are printed before break stops the loop.

3. Final Answer:

   1 2 -> Option C

4. Quick Check:

   Prints before break = 1 2 [OK]

Hint: Break stops before printing count 3 [OK]

Common Mistakes:

• Assuming count 3 is printed
• Starting count from 1 instead of 0
• Confusing break and continue effects

4. Identify the error in this Rust loop code:

for i in 1..5 {
    if i == 3 {
        continue
    }
    println!("{}", i);
}

medium

A. Missing semicolon after continue

B. Incorrect range syntax

C. println! macro is used incorrectly

D. continue cannot be used inside for loops

Solution

1. Step 1: Check syntax of continue statement

   In Rust, statements like continue require a semicolon to end the statement.

2. Step 2: Verify other parts of the code

   The range 1..5 and println! usage are correct; continue is valid inside for loops.

3. Final Answer:

   Missing semicolon after continue -> Option A

4. Quick Check:

   Statements need semicolon = A [OK]

Hint: Add semicolon after continue to fix syntax [OK]

Common Mistakes:

• Forgetting semicolon after continue
• Thinking continue is invalid in for loops
• Misreading range syntax

5. Given this Rust code, what will be the final value of sum?

let mut sum = 0;
for i in 1..6 {
    if i % 2 == 0 {
        continue;
    }
    if i == 5 {
        break;
    }
    sum += i;
}

hard

A. 4

B. 5

C. 6

D. 9

Solution

1. Step 1: Analyze loop iterations and conditions

   Loop runs i from 1 to 5 (exclusive 6). For even i, continue skips adding. For i == 5, break stops loop before adding.

2. Step 2: Calculate sum for valid i values

   i=1 (odd, add 1), i=2 (even, skip), i=3 (odd, add 3), i=4 (even, skip), i=5 (break before add). sum = 1 + 3 = 4.

3. Final Answer:

   4 -> Option A

4. Quick Check:

   Sum odd before 5 = 4 [OK]

Hint: Add only odd numbers before 5, skip evens [OK]

Common Mistakes:

• Adding even numbers mistakenly
• Including 5 in sum despite break
• Confusing continue and break effects