Checked and unchecked arithmetic in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of checked arithmetic overflow

What is the output of this C# code snippet?

C Sharp (C#)

using System;
class Program {
  static void Main() {
    try {
      int max = int.MaxValue;
      int result = checked(max + 1);
      Console.WriteLine(result);
    } catch (OverflowException) {
      Console.WriteLine("Overflow caught");
    }
  }
}

A -2147483648

B 2147483648

C Overflow caught

D Compilation error

💡 Hint

Think about what happens when you add 1 to the maximum int value inside a checked block.

The checked keyword causes the runtime to throw an OverflowException when the arithmetic operation exceeds the range of the int type. Adding 1 to int.MaxValue causes overflow, so the exception is caught and "Overflow caught" is printed.

❓ Predict Output

intermediate

Unchecked arithmetic overflow result

What is the output of this C# code snippet?

C Sharp (C#)

using System;
class Program {
  static void Main() {
    int max = int.MaxValue;
    int result = unchecked(max + 1);
    Console.WriteLine(result);
  }
}

A -2147483648

B 2147483648

C Overflow caught

D Compilation error

💡 Hint

Consider what unchecked does when an integer overflows.

The unchecked keyword disables overflow checking, so the addition wraps around. Adding 1 to int.MaxValue results in int.MinValue due to overflow wrap-around.

🧠 Conceptual

advanced

Behavior difference between checked and unchecked

Which statement best describes the difference between checked and unchecked arithmetic in C#?

A checked disables overflow exceptions; unchecked enables overflow exceptions.

B checked causes overflow exceptions; unchecked ignores overflow and wraps around silently.

C checked and unchecked both throw exceptions on overflow.

D checked and unchecked both ignore overflow and wrap around silently.

💡 Hint

Think about what happens when an integer operation exceeds its limits in each mode.

The checked keyword enables overflow checking and throws exceptions on overflow. The unchecked keyword disables overflow checking and allows wrap-around without exceptions.

❓ Predict Output

advanced

Output of mixed checked and unchecked blocks

What is the output of this C# program?

C Sharp (C#)

using System;
class Program {
  static void Main() {
    int x = int.MaxValue;
    try {
      unchecked {
        x = x + 1;
      }
      checked {
        x = x + 1;
      }
      Console.WriteLine(x);
    } catch (OverflowException) {
      Console.WriteLine("Overflow caught");
    }
  }
}

A 2147483648

B Overflow caught

C -2147483648

D -2147483647

💡 Hint

Consider the effect of unchecked and checked blocks on the variable x.

The first addition in unchecked wraps x from int.MaxValue to int.MinValue (-2147483648). The second addition in checked tries to add 1 to int.MinValue, which is valid and results in -2147483647. However, since the first addition was unchecked, no exception occurs there. The second addition is within checked and does not overflow, so no exception is thrown. The program prints -2147483647.

❓ Predict Output

expert

Output of checked arithmetic in a method with unchecked context

What is the output of this C# program?

C Sharp (C#)

using System;
class Program {
  static int AddOneChecked(int value) {
    checked {
      return value + 1;
    }
  }
  static void Main() {
    unchecked {
      int max = int.MaxValue;
      try {
        int result = AddOneChecked(max);
        Console.WriteLine(result);
      } catch (OverflowException) {
        Console.WriteLine("Overflow caught");
      }
    }
  }
}

A Overflow caught

B -2147483648

C Compilation error

D 2147483648

💡 Hint

Remember that checked and unchecked contexts are scoped and can be nested.

Even though Main is in an unchecked context, the AddOneChecked method uses a checked block. The addition of 1 to int.MaxValue inside checked triggers an OverflowException, which is caught and prints "Overflow caught".