Operator precedence in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to correctly calculate the result using operator precedence.

C++

int result = 3 + 4 * [1];

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

A1

B5

C0

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 3 and 4 first, then multiplying by 2.

Ignoring operator precedence and calculating left to right.

The multiplication operator (*) has higher precedence than addition (+), so 4 * 2 is calculated first, then 3 is added.

2fill in blank

medium

Complete the code to correctly evaluate the expression with mixed operators.

C++

int value = (10 - 2) [1] 3 + 4;

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

A*

B/

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 3 and 4 before multiplying.

Ignoring parentheses and operator precedence.

Parentheses are evaluated first: (10 - 2) = 8. Then multiplication (*) has higher precedence than addition (+), so 8 * 3 = 24, then add 4 to get 28.

3fill in blank

hard

Fix the error in the expression to get the correct result.

C++

int result = 20 / 4 [1] 2;

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

A-

B*

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or subtraction instead of multiplication.

Assuming multiplication has higher precedence than division.

Division and multiplication have the same precedence and are evaluated left to right. So 20 / 4 = 5, then 5 * 2 = 10.

4fill in blank

hard

Fill both blanks to correctly compute the expression using operator precedence.

C++

int x = 5 + 3 [1] 2 [2] 4;

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Doing addition before multiplication.

Mixing up subtraction and division.

Multiplication (*) has higher precedence, so 3 * 2 = 6. Then subtraction (-) is done: 6 - 4 = 2. Finally, addition: 5 + 2 = 7.

5fill in blank

hard

Fill all three blanks to correctly evaluate the complex expression.

C++

int result = (8 [1] 4) [2] 2 [3] 3;

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

A+

B*

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Ignoring parentheses.

Doing multiplication before division regardless of order.

Mixing up operator precedence.

First, inside parentheses: 8 - 4 = 4. Then division and multiplication have the same precedence and are evaluated left to right: 4 / 2 = 2, then 2 * 3 = 6.

Practice

1. Which operator has the highest precedence in the expression 3 + 4 * 5?

easy

A. Addition (+)

B. Subtraction (-)

C. Multiplication (*)

D. Division (/)

Solution

1. Step 1: Identify operators in the expression

   The expression has addition (+) and multiplication (*).

2. Step 2: Recall operator precedence rules

   Multiplication (*) has higher precedence than addition (+), so it is evaluated first.

3. Final Answer:

   Multiplication (*) -> Option C

4. Quick Check:

   Multiplication before addition = Multiplication (*) [OK]

Hint: Multiplication and division come before addition and subtraction [OK]

Common Mistakes:

• Thinking addition runs before multiplication
• Ignoring operator precedence rules
• Assuming left-to-right always applies

2. Which of the following expressions is syntactically correct in C++?

easy

A. int x = 5 + (3 * 2);

B. int x = 5 + 3 *;

C. int x = 5 + *3;

D. int x = 5 + 3 * 2);

Solution

1. Step 1: Check each expression for syntax errors

   int x = 5 + *3; has an invalid use of * before 3. int x = 5 + 3 *; ends with * which is incomplete. int x = 5 + 3 * 2); has an unmatched closing parenthesis.

2. Step 2: Confirm correct syntax

   int x = 5 + (3 * 2); uses parentheses correctly and has valid operators and operands.

3. Final Answer:

   int x = 5 + (3 * 2); -> Option A

4. Quick Check:

   Valid syntax with parentheses and operators = int x = 5 + (3 * 2); [OK]

Hint: Check for balanced parentheses and proper operator placement [OK]

Common Mistakes:

• Misplacing operators without operands
• Unbalanced parentheses
• Using operators incorrectly

3. What is the output of the following code?

int a = 2, b = 3, c = 4;
int result = a + b * c / a - b;
std::cout << result;

medium

A. 5

B. 2

C. 4

D. 3

Solution

1. Step 1: Evaluate multiplication and division first

   b * c = 3 * 4 = 12; then 12 / a = 12 / 2 = 6.

2. Step 2: Evaluate addition and subtraction left to right

   a + 6 = 2 + 6 = 8; then 8 - b = 8 - 3 = 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Multiplication/division before addition/subtraction = 5 [OK]

Hint: Do * and / before + and -, left to right [OK]

Common Mistakes:

• Adding before multiplying
• Ignoring division precedence
• Calculating subtraction before addition

4. Find the error in the following code snippet:

int x = 10;
int y = 5;
int z = x + y * / 2;
std::cout << z;

medium

A. Division by zero error

B. Syntax error due to misplaced operator

C. Logical error in calculation

D. No error, code runs fine

Solution

1. Step 1: Analyze the expression for syntax correctness

   The expression x + y * / 2 has two operators (*) and (/) together without an operand, which is invalid syntax.

2. Step 2: Confirm the error type

   This causes a syntax error because the compiler cannot parse the expression correctly.

3. Final Answer:

   Syntax error due to misplaced operator -> Option B

4. Quick Check:

   Invalid operator sequence causes syntax error [OK]

Hint: Check operator placement for missing operands [OK]

Common Mistakes:

• Assuming code runs despite syntax errors
• Confusing syntax error with runtime error
• Ignoring operator adjacency rules

5. Consider the expression int result = 10 - 3 * 2 + 4 / 2;. How can you change it using parentheses to make addition happen before multiplication and division?

hard

A. int result = 10 - ((3 * 2) + 4) / 2;

B. int result = ((10 - 3) * 2 + 4) / 2;

C. int result = 10 - ((3 * 2) + (4 / 2));

D. int result = 10 - (3 * (2 + 4)) / 2;

Solution

1. Step 1: Understand original precedence

   Original expression evaluates multiplication and division before addition and subtraction.

2. Step 2: Use parentheses to force addition before multiplication/division

   int result = 10 - (3 * (2 + 4)) / 2; groups (2 + 4) first, so addition happens before multiplication and division.

3. Final Answer:

   int result = 10 - (3 * (2 + 4)) / 2; -> Option D

4. Quick Check:

   Parentheses change order to add before multiply/divide [OK]

Hint: Use parentheses to group additions before other ops [OK]

Common Mistakes:

• Misplacing parentheses changing meaning
• Not grouping addition properly
• Assuming left-to-right overrides precedence