Type casting in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of static_cast with integer to float

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

C++

int main() {
    int a = 5;
    float b = static_cast<float>(a) / 2;
    std::cout << b << std::endl;
    return 0;
}

A 2.0

B 2

C Compilation error

D 2.5

💡 Hint

Remember that static_cast changes the type before division.

Casting 'a' to float makes the division a floating-point division, so 5/2 becomes 2.5.

❓ Predict Output

intermediate

Output of reinterpret_cast on pointer

What will this C++ code print?

C++

#include <iostream>
int main() {
    int x = 65;
    char* p = reinterpret_cast<char*>(&x);
    std::cout << *p << std::endl;
    return 0;
}

A Undefined behavior

B A

C Compilation error

D 65

💡 Hint

Think about how integers are stored in memory and how char* reads bytes.

The integer 65 corresponds to ASCII 'A'. reinterpret_cast treats the int's address as char*, so *p reads the first byte, printing 'A'.

❓ Predict Output

advanced

Output of const_cast removing constness

What is the output of this code?

C++

#include <iostream>
int main() {
    const int a = 10;
    int* p = const_cast<int*>(&a);
    *p = 20;
    std::cout << a << std::endl;
    return 0;
}

A Undefined behavior

B 20

C Compilation error

D 10

💡 Hint

Modifying a const variable via const_cast is risky.

Changing a const variable through const_cast causes undefined behavior, so output is unpredictable.

❓ Predict Output

advanced

Output of dynamic_cast with polymorphism

What will this code print?

C++

#include <iostream>
class Base { public: virtual ~Base() {} };
class Derived : public Base {};
int main() {
    Base* b = new Base();
    Derived* d = dynamic_cast<Derived*>(b);
    if (d) std::cout << "Derived" << std::endl;
    else std::cout << "Null" << std::endl;
    delete b;
    return 0;
}

A Null

B Runtime error

C Compilation error

D Derived

💡 Hint

dynamic_cast returns nullptr if cast fails.

Since 'b' points to Base, not Derived, dynamic_cast returns nullptr, so output is 'Null'.

🧠 Conceptual

expert

Which cast is safest for downcasting polymorphic types?

In C++, when you want to safely convert a base class pointer to a derived class pointer, which cast should you use?

A static_cast

B reinterpret_cast

C dynamic_cast

D const_cast

💡 Hint

Consider runtime type checking.

dynamic_cast performs runtime checks and returns nullptr if the cast is invalid, making it safe for downcasting.

Practice

1. What does static_cast<int>(3.14) do in C++?

easy

A. Leaves the value unchanged as 3.14

B. Converts the integer 3 to the floating-point number 3.14

C. Causes a runtime error

D. Converts the floating-point number 3.14 to the integer 3

Solution

1. Step 1: Understand static_cast usage

   static_cast<int> converts a value to an integer type explicitly.

2. Step 2: Apply static_cast to 3.14

   The floating-point number 3.14 is converted to integer by dropping the decimal part, resulting in 3.

3. Final Answer:

   Converts the floating-point number 3.14 to the integer 3 -> Option D

4. Quick Check:

   static_cast<int>(3.14) = 3 [OK]

Hint: static_cast truncates decimals when converting float to int [OK]

Common Mistakes:

• Thinking it rounds the number instead of truncating
• Confusing static_cast with dynamic_cast
• Expecting a runtime error from static_cast

2. Which of the following is the correct syntax for casting a double variable d to int using static_cast?

easy

A. int i = (int)static_cast(d);

B. int i = static_cast<int>(d);

C. int i = static_cast(d, int);

D. int i = static_cast<int>d;

Solution

1. Step 1: Recall static_cast syntax

   The correct syntax is static_cast<type>(expression).

2. Step 2: Match syntax with options

   int i = static_cast<int>(d); matches the correct syntax: int i = static_cast<int>(d);.

3. Final Answer:

   int i = static_cast<int>(d); -> Option B

4. Quick Check:

   Correct static_cast syntax = int i = static_cast<int>(d); [OK]

Hint: Use angle brackets for type in static_cast [OK]

Common Mistakes:

• Using parentheses instead of angle brackets for type
• Placing type after variable instead of inside <>
• Mixing C-style cast syntax with static_cast

3. What is the output of the following C++ code?

double x = 9.99;
int y = static_cast<int>(x);
std::cout << y << std::endl;

medium

A. 9.99

B. 10

C. 9

D. Compilation error

Solution

1. Step 1: Understand static_cast behavior on double to int

   static_cast truncates the decimal part, so 9.99 becomes 9.

2. Step 2: Predict output of std::cout

   The integer 9 is printed to the console.

3. Final Answer:

   9 -> Option C

4. Quick Check:

   static_cast<int>(9.99) = 9 [OK]

Hint: Casting double to int drops decimals, no rounding [OK]

Common Mistakes:

• Expecting rounding to 10 instead of truncation
• Confusing output type with original double
• Thinking static_cast causes compile error here

4. Identify the error in this code snippet:

float f = 3.5f;
int i = static_cast<int> f;
std::cout << i;

medium

A. Missing parentheses after static_cast<int>

B. Cannot cast float to int using static_cast

C. Variable i is not declared

D. Missing semicolon after float declaration

Solution

1. Step 1: Check static_cast syntax

   static_cast requires parentheses around the value to cast, like static_cast<int>(f).

2. Step 2: Identify missing parentheses

   The code misses parentheses after static_cast<int>, causing syntax error.

3. Final Answer:

   Missing parentheses after static_cast<int> -> Option A

4. Quick Check:

   static_cast<int>(f) needs parentheses [OK]

Hint: Always use parentheses after static_cast type [OK]

Common Mistakes:

• Omitting parentheses after static_cast
• Thinking static_cast can't convert float to int
• Ignoring compiler error messages

5. Given the code below, what will be the output?

int a = 65;
char c = static_cast<char>(a);
std::cout << c << std::endl;

Note: ASCII value 65 corresponds to 'A'.

hard

A. 'A'

B. Compilation error

C. 65

D. Undefined behavior

Solution

1. Step 1: Understand static_cast from int to char

   static_cast converts the integer 65 to its corresponding ASCII character 'A'.

2. Step 2: Predict output of std::cout

   Printing the char variable outputs the character 'A'.

3. Final Answer:

   'A' -> Option A

4. Quick Check:

   static_cast<char>(65) = 'A' [OK]

Hint: Casting int to char prints ASCII character [OK]

Common Mistakes:

• Expecting numeric 65 to print instead of 'A'
• Thinking casting int to char causes error
• Confusing char with string output