Arithmetic operators in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of mixed arithmetic operations

What is the output of the following Java code?

Java

public class Main {
    public static void main(String[] args) {
        int a = 10;
        int b = 3;
        int result = a / b * b + a % b;
        System.out.println(result);
    }
}

A 12

B 9

C 10

D 13

💡 Hint

Remember the order of operations and how integer division works in Java.

Integer division a / b equals 3 (since 10 / 3 = 3). Then 3 * b = 9. The remainder a % b is 1. Adding 9 + 1 gives 10.

❓ Predict Output

intermediate

Result of arithmetic with doubles

What is the output of this Java program?

Java

public class Main {
    public static void main(String[] args) {
        double x = 5.0 / 2;
        double y = 5 / 2.0;
        System.out.println(x + "," + y);
    }
}

A 2.5,2.5

B 2,2

C 2,2.5

D 2.0,2.0

💡 Hint

Check how Java handles division when one operand is a double.

Both divisions involve a double operand, so the division is floating-point, resulting in 2.5 for both.

❓ Predict Output

advanced

Output of complex arithmetic expression with increment operators

What is the output of this Java code snippet?

Java

public class Main {
    public static void main(String[] args) {
        int i = 1;
        int result = i++ + ++i * i++;
        System.out.println(result);
    }
}

A 9

B 12

C 11

D 10

💡 Hint

Evaluate the increments step by step, remembering post-increment and pre-increment behavior.

i++ uses i=1 then increments to 2; ++i increments to 3 then uses 3; i++ uses 3 then increments to 4. Expression: 1 + 3 * 3 = 1 + 9 = 10. Stepwise: i=1; i++=1 (i=2); ++i=3 (i=3); i++=3 (i=4); expression=1 + 3*3=10. Output is 10.

❓ Predict Output

advanced

Division by zero with floating point

What is the output of this Java program?

Java

public class Main {
    public static void main(String[] args) {
        double a = 5.0 / 0;
        System.out.println(a);
    }
}

A ArithmeticException

B Infinity

C NaN

D 0

💡 Hint

Division by zero behaves differently for integers and floating-point numbers in Java.

Dividing a floating-point number by zero results in Infinity, not an exception.

🧠 Conceptual

expert

Number of items in a map after arithmetic key operations

Consider this Java code snippet. How many entries does the map contain after execution?

Java

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        Map<Integer, Integer> map = new HashMap<>();
        int x = 2;
        map.put(x + 1, x * 2);
        map.put(x++, x + 3);
        map.put(++x, x * x);
        System.out.println(map.size());
    }
}

A 3

B 2

C 1

D 4

💡 Hint

Track the value of x carefully and note that keys may overwrite existing entries.

Stepwise: x=2 map.put(3,4) // key=3, value=4 map.put(2,5) // x++ uses 2 then x=3, value=5 map.put(4,16) // ++x increments x to 4, value=16 Keys are 3,2,4 distinct, so map size is 3.

Practice

1. Which of the following is the correct symbol for the modulus operator in Java, which gives the remainder of a division?

easy

A. *

B. /

C. -

D. %

Solution

1. Step 1: Understand the modulus operator

   The modulus operator returns the remainder after division of two numbers.

2. Step 2: Identify the correct symbol in Java

   In Java, the symbol for modulus is %.

3. Final Answer:

   % -> Option D

4. Quick Check:

   Modulus operator = % [OK]

Hint: Modulus operator is always % in Java math [OK]

Common Mistakes:

• Confusing modulus % with division /
• Using * or - instead of %
• Thinking modulus returns quotient

2. Which of the following Java statements correctly calculates the product of two integers a and b?

easy

A. int result = a / b;

B. int result = a + b;

C. int result = a * b;

D. int result = a % b;

Solution

1. Step 1: Identify the multiplication operator

   In Java, the multiplication operator is *.

2. Step 2: Check the statement that uses multiplication

   The statement int result = a * b; correctly multiplies a and b.

3. Final Answer:

   int result = a * b; -> Option C

4. Quick Check:

   Multiplication operator = * [OK]

Hint: Use * for multiplication in Java expressions [OK]

Common Mistakes:

• Using + instead of * for multiplication
• Confusing division / with multiplication
• Using % which is remainder, not product

3. What is the output of the following Java code?

int x = 10;
int y = 3;
System.out.println(x / y);

medium

A. 3

B. 3.3333333

C. 3.0

D. 4

Solution

1. Step 1: Understand integer division in Java

   Both x and y are integers, so division drops the decimal part.

2. Step 2: Calculate integer division result

   10 divided by 3 is 3.333..., but integer division returns 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Integer division drops decimals = 3 [OK]

Hint: Integer division drops decimals, result is integer [OK]

Common Mistakes:

• Expecting decimal output with int division
• Confusing / with % operator
• Assuming automatic float conversion

4. Identify the error in the following Java code snippet:

int a = 5;
int b = 0;
int c = a / b;
System.out.println(c);

medium

A. Division by zero causes runtime error

B. Variable c is not declared

C. Missing semicolon after declaration

D. Incorrect use of modulus operator

Solution

1. Step 1: Analyze the division operation

   The code divides a by b, where b is zero.

2. Step 2: Understand division by zero in Java

   Dividing an integer by zero causes a runtime ArithmeticException error.

3. Final Answer:

   Division by zero causes runtime error -> Option A

4. Quick Check:

   Division by zero throws error [OK]

Hint: Never divide by zero; it crashes the program [OK]

Common Mistakes:

• Ignoring division by zero error
• Thinking it returns zero or infinity
• Confusing syntax error with runtime error

5. Given the code below, what will be the value of result after execution?

int a = 15;
int b = 4;
int result = a / b + a % b * 2;

hard

A. 11

B. 9

C. 8

D. 7

Solution

1. Step 1: Calculate integer division and modulus

   15 / 4 = 3 (integer division), 15 % 4 = 3 (remainder).

2. Step 2: Apply operator precedence and compute expression

   Expression is 3 + 3 * 2. Multiplication first: 3 * 2 = 6. Then addition: 3 + 6 = 9.

3. Step 3: Re-check calculation

   Wait, re-check: 15 / 4 = 3, 15 % 4 = 3, 3 * 2 = 6, 3 + 6 = 9.

4. Final Answer:

   9 -> Option B

5. Quick Check:

   Division + (modulus * 2) = 9 [OK]

Hint: Remember * before + in mixed expressions [OK]

Common Mistakes:

• Adding before multiplying
• Confusing division and modulus results
• Forgetting integer division truncates decimals