Operator precedence - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to correctly calculate the expression result.

C

int result = 5 + 3 [1] 2;

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

A+

B-

C/

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of * causes the addition to happen first, changing the result.

Using - or / changes the intended calculation.

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

2fill in blank

medium

Complete the code to correctly evaluate the expression with parentheses.

C

int value = (4 + 6) [1] 3;

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Ignoring parentheses and multiplying 6 * 3 first.

Using addition instead of multiplication after parentheses.

Parentheses force 4 + 6 to be calculated first, then multiplied by 3.

3fill in blank

hard

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

C

int output = 10 - 4 [1] 2;

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 calculation order.

Using / divides instead of multiplying.

Multiplication (*) has higher precedence than subtraction, so 4 * 2 is done first.

4fill in blank

hard

Fill both blanks to correctly compute the expression with mixed operators.

C

int result = 8 [1] 2 [2] 3;

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Placing addition before multiplication changes the result.

Using subtraction instead of addition changes the final value.

Multiplication (*) is done before addition (+), so 8 * 2 is calculated first, then 3 is added.

5fill in blank

hard

Fill all three blanks to correctly evaluate the complex expression.

C

int final = 12 [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

Changing the order of operations by using wrong operators.

Ignoring left-to-right evaluation for operators with same precedence.

Division (/) and multiplication (*) have higher precedence and are done left to right, then subtraction (-) is last.

Practice

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

easy

A. Division (/)

B. Addition (+)

C. Subtraction (-)

D. Multiplication (*)

Solution

1. Step 1: Recall operator precedence rules

   Multiplication and division have higher precedence than addition and subtraction in C.

2. Step 2: Identify operators in the expression

   The expression has addition (+) and multiplication (*). Multiplication runs first.

3. Final Answer:

   Multiplication (*) -> Option D

4. Quick Check:

   Multiplication > Addition [OK]

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

Common Mistakes:

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

2. Which of the following 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 the desired calculation

   Add 2 and 3 first, then multiply by 4.

2. Step 2: Check parentheses usage

   Only (2 + 3) * 4 uses parentheses to add 2 and 3 first, then multiply by 4.

3. Final Answer:

   (2 + 3) * 4 -> Option A

4. Quick Check:

   Parentheses change order to add first [OK]

Hint: Use parentheses to force addition before multiplication [OK]

Common Mistakes:

• Ignoring parentheses and trusting default precedence
• Misreading the expression order
• Assuming left to right overrides precedence

3. What is the output of this C code?

int x = 5 + 3 * 2 - 4 / 2;
printf("%d", x);

medium

A. 10

B. 9

C. 11

D. 8

Solution

1. Step 1: Apply operator precedence

   Multiplication and division first: 3 * 2 = 6, 4 / 2 = 2.

2. Step 2: Calculate the expression left to right

   Expression becomes 5 + 6 - 2 = 9.

3. Final Answer:

   9 -> Option B

4. Quick Check:

   5 + 6 - 2 = 9 [OK]

Hint: Calculate * and / before + and - [OK]

Common Mistakes:

• Adding before multiplying
• Dividing after subtraction
• Calculating left to right ignoring precedence

4. Identify the error in this expression:

int result = 10 / 2 * 3 + 4 - 5;

medium

A. Multiplication and division have the same precedence and are left to right

B. Subtraction should be done before multiplication

C. Addition has higher precedence than multiplication

D. Division should be done after addition

Solution

1. Step 1: Check operator precedence and associativity

   Multiplication (*) and division (/) have the same precedence and are evaluated left to right.

2. Step 2: Verify the expression evaluation order

   Expression evaluates as ((10 / 2) * 3) + 4 - 5, which is correct.

3. Final Answer:

   Multiplication and division have the same precedence and are left to right -> Option A

4. Quick Check:

   * and / same precedence, left to right [OK]

Hint: Remember * and / are equal precedence, evaluated left to right [OK]

Common Mistakes:

• Thinking division happens after addition
• Assuming addition has higher precedence
• Ignoring left-to-right rule for same precedence

5. Given the expression int y = 8 - 3 + 2 * 4 / 2;, which parentheses placement changes the result to 14?

hard

A. 8 - 3 + (2 * 4) / 2

B. 8 - (3 + 2) * 4 / 2

C. (8 - 3 + 2) * 4 / 2

D. (8 - (3 + 2)) * 4 / 2

Solution

1. Step 1: Calculate original expression

   * and / first left-to-right: 2 * 4 = 8, 8 / 2 = 4; then 8 - 3 + 4 = 9.

2. Step 2: Evaluate (8 - 3 + 2) * 4 / 2

   (8 - 3 + 2) = 7, 7 * 4 = 28, 28 / 2 = 14.

3. Step 3: Confirm others

   8 - (3 + 2) * 4 / 2 = 8 - 20 / 2 = 8 - 10 = -2; 8 - 3 + (2 * 4) / 2 = 9; (8 - (3 + 2)) * 4 / 2 = 3 * 4 / 2 = 6.

4. Final Answer:

   (8 - 3 + 2) * 4 / 2 -> Option C

5. Quick Check:

   Parentheses force addition before multiplication [OK]

Hint: Try parentheses around addition to change multiplication order [OK]

Common Mistakes:

• Assuming original order always applies
• Not recalculating expression after adding parentheses
• Misplacing parentheses without recalculating