Operator precedence in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of mixed arithmetic and bitwise operators

What is the output of the following C++ code snippet?

C++

#include <iostream>
int main() {
    int a = 5, b = 3, c = 2;
    int result = a + b << c;
    std::cout << result << std::endl;
    return 0;
}

A 32

B 14

C 13

D 16

💡 Hint

Remember that '+' has higher precedence than '<<'.

The expression is evaluated as (a + b) << c = (5 + 3) << 2 = 8 << 2 = 32.

❓ Predict Output

intermediate

Output of logical and bitwise operators combined

What is the output of this C++ code?

C++

#include <iostream>
int main() {
    int x = 1, y = 2, z = 3;
    int result = x & y || z;
    std::cout << result << std::endl;
    return 0;
}

A 3

B 0

C 1

D 2

💡 Hint

Check operator precedence between '&' and '||'.

Bitwise AND '&' has higher precedence than logical OR '||'. So x & y is 1 & 2 = 0, then 0 || 3 is true (1). So output is 1.

❓ Predict Output

advanced

Result of complex expression with multiple operators

What is the output of this C++ program?

C++

#include <iostream>
int main() {
    int a = 4, b = 2, c = 3;
    int result = a - b * c >> 1 + 1;
    std::cout << result << std::endl;
    return 0;
}

A -1

B 1

C 0

D 2

💡 Hint

Remember operator precedence: '*' then '-' then '>>' then '+'.

Multiplication first: b * c = 2 * 3 = 6. Then subtraction: a - 6 = 4 - 6 = -2. Then addition in shift amount: 1 + 1 = 2. Then right shift: -2 >> 2. In C++ right shift of negative numbers is implementation-defined but usually arithmetic shift keeps sign, resulting in -1.

❓ Predict Output

advanced

Output of expression with ternary and logical operators

What is the output of this C++ code?

C++

#include <iostream>
int main() {
    int x = 0, y = 5;
    int result = x ? y : y > 3 ? 10 : 20;
    std::cout << result << std::endl;
    return 0;
}

A 5

B 0

C 20

D 10

💡 Hint

Ternary operators associate right to left.

Expression is x ? y : (y > 3 ? 10 : 20). Since x is 0 (false), evaluate y > 3 ? 10 : 20. y=5 > 3 is true, so result is 10.

🧠 Conceptual

expert

Operator precedence and associativity in complex expression

Consider the expression:

int x = 2, y = 3, z = 4;
int result = x + y * z / y - z % x;

Which of the following correctly describes the order in which the operations are performed?

A Multiplication and division first (left to right), then addition and subtraction (left to right), then modulo last

B Multiplication, division, and modulo first (left to right), then addition and subtraction (left to right)

C Addition first, then multiplication and division, then subtraction and modulo

D Modulo first, then multiplication and division, then addition and subtraction

💡 Hint

Check operator precedence table: *, /, % have same precedence and associate left to right.

Multiplication (*), division (/), and modulo (%) have the same precedence and associate left to right, so they are evaluated first in order from left to right. Then addition (+) and subtraction (-) are evaluated left to right.

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