Operator precedence - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of mixed arithmetic and bitwise operators

What is the output of this C code snippet?

C

int main() {
    int a = 5, b = 3, c = 2;
    int result = a + b << c;
    printf("%d", result);
    return 0;
}

A 14

B 16

C 32

D 13

💡 Hint

Remember that bitwise shift operators have lower precedence than addition.

The expression is evaluated as (a + b) << c = (5 + 3) << 2 = 8 << 2 = 32, since + has higher precedence than <<. The output is 32.

❓ Predict Output

intermediate

Output of logical and bitwise operators combined

What is the output of this C code?

C

int main() {
    int x = 1, y = 0;
    int z = x && y & x;
    printf("%d", z);
    return 0;
}

A 0

B 1

C 2

D 3

💡 Hint

Check operator precedence between && and & operators.

The & operator has higher precedence than &&, so y & x is evaluated first: 0 & 1 = 0. Then x && 0 is evaluated: 1 && 0 = 0. So the output is 0.

❓ Predict Output

advanced

Result of complex expression with mixed operators

What is the output of this C program?

C

int main() {
    int a = 4, b = 2, c = 3;
    int result = a - b * c / b + c;
    printf("%d", result);
    return 0;
}

A 4

B 7

C 3

D 9

💡 Hint

Remember multiplication and division have higher precedence than addition and subtraction.

First, b * c / b = (2 * 3) / 2 = 6 / 2 = 3 (left-to-right). Then a - 3 + c = 4 - 3 + 3 = 4 (left-to-right for - and +). The output is 4.

❓ Predict Output

advanced

Output of expression with ternary and logical operators

What does this C code print?

C

int main() {
    int x = 0, y = 5;
    int z = x ? y : y > 3 ? 10 : 20;
    printf("%d", z);
    return 0;
}

A 5

B 10

C 20

D 0

💡 Hint

Ternary operators associate right to left. Evaluate carefully.

Since x is 0 (false), the expression evaluates the second ternary: y > 3 ? 10 : 20. y is 5, which is greater than 3, so the result is 10.

❓ Predict Output

expert

Value of variable after complex expression with increments and precedence

What is the value of variable x after running this C code?

C

int main() {
    int x = 3;
    int y = x++ * ++x + x-- - --x;
    printf("%d", x);
    return 0;
}

A 2

B 1

C 4

D 3

💡 Hint

Remember the order of evaluation and side effects of post and pre increments.

This expression has undefined behavior due to multiple modifications to x without sequence points. Assuming left-to-right operand evaluation (common in many compilers): - x++: uses 3, x=4 - ++x: x=5, uses 5 - x++ * ++x = 3*5=15 - x--: uses 5, x=4 - --x: x=3, uses 3 - 15 + 5 - 3 = 17 (y=17) Final x=3, prints 3.

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