Assignment operators in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add 5 to the variable x using an assignment operator.

Rust

let mut x = 10;
x [1] 5;
println!("{}", x);

Drag options to blanks, or click blank then click option'

A+=

B-=

C*=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' will subtract instead of add.

Forgetting to make the variable mutable with 'mut'.

The operator '+=' adds the right value to the variable and assigns the result back to it.

2fill in blank

medium

Complete the code to multiply the variable y by 3 using an assignment operator.

Rust

let mut y = 4;
y [1] 3;
println!("{}", y);

Drag options to blanks, or click blank then click option'

A-=

B/=

C+=

D*=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' or '-=' instead of '*=' changes the operation.

Not declaring the variable as mutable.

The '*=' operator multiplies the variable by the right value and assigns the result back to it.

3fill in blank

hard

Fix the error in the code by choosing the correct assignment operator to divide z by 2.

Rust

let mut z = 20;
z [1] 2;
println!("{}", z);

Drag options to blanks, or click blank then click option'

A+=

B*=

C/=

D-=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*=' multiplies instead of dividing.

Using '+=' or '-=' changes the operation.

The '/=' operator divides the variable by the right value and assigns the result back to it.

4fill in blank

hard

Fill both blanks to subtract 7 from a and then add 10 to b using assignment operators.

Rust

let mut a = 15;
let mut b = 5;
a [1] 7;
b [2] 10;
println!("{} {}", a, b);

Drag options to blanks, or click blank then click option'

A-=

B+=

C*=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up '+' and '-' operators.

Using '*=' or '/=' instead of addition or subtraction.

Use '-=' to subtract from 'a' and '+=' to add to 'b'.

5fill in blank

hard

Fill all three blanks to multiply m by 4, divide n by 2, and add 3 to p using assignment operators.

Rust

let mut m = 3;
let mut n = 8;
let mut p = 1;
m [1] 4;
n [2] 2;
p [3] 3;
println!("{} {} {}", m, n, p);

Drag options to blanks, or click blank then click option'

A+=

B/=

D*=

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing the order of operators.

Using the wrong operator for the intended operation.

Use '*=' to multiply 'm', '/=' to divide 'n', and '+=' to add to 'p'.

Practice

1. What does the Rust assignment operator += do?

easy

A. Subtracts the right value from the left variable and stores the result in the variable

B. Adds the right value to the left variable and stores the result in the variable

C. Multiplies the right value with the left variable and stores the result in the variable

D. Divides the left variable by the right value and stores the result in the variable

Solution

1. Step 1: Understand the += operator

   The += operator adds the right-hand side value to the left-hand side variable.

2. Step 2: Effect on the variable

   The result of the addition is stored back into the same variable, updating its value.

3. Final Answer:

   Adds the right value to the left variable and stores the result in the variable -> Option B

4. Quick Check:

   += means add and assign [OK]

Hint: Think: add then store back in the same variable [OK]

Common Mistakes:

• Confusing += with subtraction or multiplication
• Forgetting that the variable must be mutable
• Thinking it creates a new variable instead of updating

2. Which of the following is the correct way to use the *= operator in Rust?

easy

A. let x = 5; x *= 2;

B. let mut x = 5; *= x 2;

C. let x = 5; mut x *= 2;

D. let mut x = 5; x *= 2;

Solution

1. Step 1: Check variable mutability

   In Rust, to change a variable's value, it must be declared with mut. So let mut x = 5; is correct.

2. Step 2: Correct operator usage

   The operator *= is used as x *= 2; to multiply and assign.

3. Final Answer:

   let mut x = 5; x *= 2; -> Option D

4. Quick Check:

   Mutable variable + operator syntax = correct [OK]

Hint: Declare variable mutable before using assignment operators [OK]

Common Mistakes:

• Not declaring variable as mutable
• Placing mut in wrong position
• Incorrect operator syntax like *= x 2

3. What is the output of the following Rust code?

let mut a = 10;
a += 5;
a *= 2;
println!("{}", a);

medium

A. 30

B. 25

C. 20

D. 15

Solution

1. Step 1: Perform a += 5;

   Starting with a = 10, adding 5 gives a = 15.

2. Step 2: Perform a *= 2;

   Multiplying 15 by 2 updates a = 30.

3. Final Answer:

   30 -> Option A

4. Quick Check:

   10 + 5 = 15; 15 * 2 = 30 [OK]

Hint: Calculate step-by-step updates to variable [OK]

Common Mistakes:

• Adding and multiplying in wrong order
• Forgetting variable is mutable
• Misreading operator effects

4. Identify the error in this Rust code snippet:

let x = 8;
x -= 3;
println!("{}", x);

medium

A. The println! macro is used incorrectly

B. The operator -= is not valid in Rust

C. Variable x is not mutable but is modified

D. Missing semicolon after println!

Solution

1. Step 1: Check variable mutability

   The variable x is declared without mut, so it is immutable.

2. Step 2: Check assignment operator usage

   The operator -= tries to subtract and assign a new value to x, which is not allowed for immutable variables.

3. Final Answer:

   Variable x is not mutable but is modified -> Option C

4. Quick Check:

   Immutable variable cannot be changed [OK]

Hint: Mutable variables needed for assignment operators [OK]

Common Mistakes:

• Assuming all variables are mutable by default
• Thinking operator syntax is wrong
• Ignoring Rust's immutability rules

5. Given the code below, what is the final value of result?

let mut result = 50;
let change = 7;
result %= change;
result += 3;
result *= 4;

hard

A. 16

B. 12

C. 28

D. 14

Solution

1. Step 1: Calculate result %= change;

   50 % 7 equals 1 because 7 * 7 = 49 and remainder is 1, so result = 1.

2. Step 2: Calculate result += 3;

   Add 3 to 1 gives result = 4.

3. Step 3: Calculate result *= 4;

   Multiply 4 by 4 gives result = 16.

4. Final Answer:

   16 -> Option A

5. Quick Check:

   50 % 7 = 1; 1 + 3 = 4; 4 * 4 = 16 [OK]

Hint: Apply each operator stepwise carefully [OK]

Common Mistakes:

• Miscomputing modulus operation
• Skipping steps or doing operations out of order
• Choosing wrong multiplication result