Operator precedence in Rust - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Rust code involving mixed operators?

Consider the following Rust code snippet. What will it print when run?

Rust

fn main() {
    let result = 3 + 4 * 2;
    println!("{}", result);
}

A 11

B Error

C 10

D 14

💡 Hint

Remember that multiplication (*) has higher precedence than addition (+).

Multiplication happens before addition, so 4 * 2 = 8, then 3 + 8 = 11.

❓ Predict Output

intermediate

What is the output of this Rust code with logical and comparison operators?

What does this Rust program print?

Rust

fn main() {
    let a = true;
    let b = false;
    let c = a || b && false;
    println!("{}", c);
}

A true

B false

C Compilation error

D panic at runtime

💡 Hint

Logical AND (&&) has higher precedence than logical OR (||).

b && false is false, then a || false is true.

❓ Predict Output

advanced

What is the output of this Rust code with mixed bitwise and comparison operators?

Analyze the following Rust code and select the output it produces.

Rust

fn main() {
    let x = 5;
    let y = 3;
    let z = (x & y) == 1;
    println!("{}", z);
}

A false

B panic at runtime

C true

D Compilation error

💡 Hint

Bitwise AND (&) has higher precedence than equality (==).

x & y is 1, so 1 == 1 is true.

❓ Predict Output

advanced

What is the output of this Rust code with assignment and arithmetic operators?

What does this Rust program print?

Rust

fn main() {
    let mut a = 2;
    a += 3 * 4;
    println!("{}", a);
}

A 20

B 14

C Error: cannot assign to immutable variable

D 10

💡 Hint

Multiplication happens before addition assignment.

3 * 4 = 12, then a += 12 means a = 2 + 12 = 14.

❓ Predict Output

expert

What is the output of this Rust code with mixed shift and arithmetic operators?

Analyze this Rust code and select the output it produces.

Rust

fn main() {
    let a = 1 + 2 << 3;
    println!("{}", a);
}

A 9

B Compilation error

C 16

D 24

💡 Hint

Addition (+) has higher precedence than bitwise shift (<<).

1 + 2 = 3, then 3 << 3 means shifting 3 left by 3 bits = 3 * 8 = 24.

Practice

1. In Rust, which operator has the highest precedence among these: +, *, -, /?

easy

A. Multiplication (*) and division (/) have higher precedence than addition (+) and subtraction (-).

B. Addition (+) and subtraction (-) have higher precedence than multiplication (*) and division (/).

C. All operators have the same precedence and are evaluated left to right.

D. Subtraction (-) has the highest precedence among all.

Solution

1. Step 1: Recall Rust operator precedence rules

   Multiplication (*) and division (/) operators have higher precedence than addition (+) and subtraction (-).

2. Step 2: Compare given operators

   Among the given operators, * and / are evaluated before + and - in expressions.

3. Final Answer:

   Multiplication (*) and division (/) have higher precedence than addition (+) and subtraction (-). -> Option A

4. Quick Check:

   *, / > +, - [OK]

Hint: Remember: multiply/divide before add/subtract [OK]

Common Mistakes:

• Thinking addition has higher precedence than multiplication
• Assuming all operators have equal precedence
• Confusing subtraction precedence with multiplication

2. Which of the following Rust expressions is correctly written to add 2 and 3, then multiply the result by 4?

easy

A. 2 + 3 * 4

B. (2 + 3) * 4

C. 2 + (3 * 4)

D. 2 * 3 + 4

Solution

1. Step 1: Understand operator precedence and parentheses

   Multiplication (*) has higher precedence than addition (+), so without parentheses, multiplication happens first.

2. Step 2: Check each expression

   (2 + 3) * 4 uses parentheses to add 2 and 3 first, then multiplies by 4, which matches the requirement.

3. Final Answer:

   (2 + 3) * 4 -> Option B

4. Quick Check:

   Parentheses force addition first [OK]

Hint: Use parentheses to change default order [OK]

Common Mistakes:

• Ignoring parentheses and relying on default precedence
• Misplacing parentheses causing wrong order
• Assuming left-to-right always applies

3. What is the output of this Rust code?

let result = 10 - 4 / 2 + 3 * 2;
println!("{}", result);

medium

A. 13

B. 10

C. 11

D. 14

Solution

1. Step 1: Apply operator precedence to expression

   Division and multiplication happen before addition and subtraction:
   4 / 2 = 2
   3 * 2 = 6

2. Step 2: Calculate left to right with results

   Expression becomes: 10 - 2 + 6
   10 - 2 = 8
   8 + 6 = 14

3. Final Answer:

   14 -> Option D

4. Quick Check:

   */ before +- gives 14 [OK]

Hint: Calculate * and / first, then + and - left to right [OK]

Common Mistakes:

• Doing operations strictly left to right ignoring precedence
• Adding before multiplying
• Miscomputing division or multiplication

4. Identify the error in this Rust expression:

let value = 5 + 3 * / 2;

medium

A. No error, expression is valid

B. Logical error: multiplication should be addition

C. Syntax error due to misplaced operator '/'

D. Runtime error due to division by zero

Solution

1. Step 1: Analyze the expression syntax

   The expression has * / operators together without a number between them, which is invalid syntax in Rust.

2. Step 2: Confirm error type

   This causes a syntax error because Rust expects an operand between operators.

3. Final Answer:

   Syntax error due to misplaced operator '/' -> Option C

4. Quick Check:

   Operators must have operands between them [OK]

Hint: Check for missing operands between operators [OK]

Common Mistakes:

• Assuming expression is valid without checking syntax
• Confusing syntax error with runtime error
• Ignoring operator placement rules

5. Given the Rust expression:

let x = 2 + 3 * 4 - 6 / 3 + (8 - 5) * 2;

What is the correct value of x after evaluation?

hard

A. 18

B. 20

C. 19

D. 21

Solution

1. Step 1: Evaluate parentheses and high precedence operators

   Calculate inside parentheses:
   (8 - 5) = 3
   Then multiplication and division:
   3 * 4 = 12
   6 / 3 = 2
   3 * 2 = 6 (from parentheses result * 2)

2. Step 2: Substitute and calculate addition and subtraction left to right

   Expression becomes: 2 + 12 - 2 + 6
   2 + 12 = 14
   14 - 2 = 12
   12 + 6 = 18

3. Final Answer:

   18 -> Option A

4. Quick Check:

   Parentheses and */ first, then +- left to right [OK]

Hint: Calculate parentheses first, then * and /, then + and - left to right [OK]

Common Mistakes:

• Ignoring parentheses and calculating in wrong order
• Doing addition before multiplication
• Mixing up left-to-right evaluation for + and -