Operator precedence - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is operator precedence in C?

Operator precedence determines the order in which operators are evaluated in an expression. Operators with higher precedence are evaluated before those with lower precedence.

beginner

Which operator has higher precedence: * (multiplication) or + (addition)?

The multiplication operator * has higher precedence than the addition operator +. So, in 3 + 4 * 5, the multiplication happens first.

intermediate

What does associativity mean in operator precedence?

Associativity defines the direction in which operators of the same precedence are evaluated. For example, left-to-right means operators are evaluated from left to right.

beginner

How does parentheses ( ) affect operator precedence?

Parentheses have the highest precedence. Expressions inside parentheses are evaluated first, no matter what other operators are present.

beginner

In the expression a = b + c * d;, which operation happens first?

The multiplication c * d happens first because * has higher precedence than +. Then the result is added to b, and finally assigned to a.

Which operator has the highest precedence in C?

A Parentheses ( )

B Addition (+)

C Assignment (=)

D Logical AND (&&)

Parentheses have the highest precedence and force the expression inside them to be evaluated first.

What is the associativity of the subtraction operator (-) in C?

A Left to right

B No associativity

C Right to left

D Depends on compiler

Subtraction has left-to-right associativity, so expressions like 10 - 5 - 2 are evaluated as (10 - 5) - 2.

In the expression 5 + 3 * 2, what is the result?

A 13

B 16

C 10

D 11

Multiplication happens first: 3 * 2 = 6, then addition: 5 + 6 = 11.

Which operator has lower precedence than multiplication (*)?

A Division (/)

B Addition (+)

C Modulo (%)

D Unary minus (-)

Addition (+) has lower precedence than multiplication (*), division (/), and modulo (%).

What happens first in a = (b + c) * d;?

A Multiplication

B Assignment

C Addition inside parentheses

D Evaluation from right to left

Parentheses force the addition (b + c) to happen before multiplication.

Explain operator precedence and how it affects the evaluation of expressions in C.

Think about which operations happen first in a math expression.

Describe the role of parentheses in changing operator precedence.

How do parentheses help control the order of operations?

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