Type casting in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to convert the integer 10 to a float.

C++

int a = 10;
float b = [1];
std::cout << b << std::endl;

Drag options to blanks, or click blank then click option'

Astatic_cast<float>(a)

B(int)a

Cfloat(a)

Da

Attempts:

3 left

💡 Hint

Common Mistakes

Using C-style cast like (int)a which does not convert to float.

Assigning integer directly without casting.

Use static_cast<float>(a) to convert integer a to float safely in C++.

2fill in blank

medium

Complete the code to cast a double to an integer using C-style cast.

C++

double pi = 3.14159;
int x = [1];
std::cout << x << std::endl;

Drag options to blanks, or click blank then click option'

Astatic_cast<int>(pi)

B(int)pi

Cint(pi)

Dpi

Attempts:

3 left

💡 Hint

Common Mistakes

Using int(pi) which is a functional-style cast instead of C-style.

Assigning double directly to int without cast.

C-style cast (int)pi converts the double pi to an integer by truncating the decimal part.

3fill in blank

hard

Fix the error in the code by correctly casting a void pointer to an int pointer.

C++

void* ptr = nullptr;
int* iptr = [1];
std::cout << iptr << std::endl;

Drag options to blanks, or click blank then click option'

Areinterpret_cast<int*>(ptr)

Bstatic_cast<int*>(ptr)

C(int*)ptr

Ddynamic_cast<int*>(ptr)

Attempts:

3 left

💡 Hint

Common Mistakes

Using dynamic_cast which only works with polymorphic types.

Using C-style cast which is less safe.

Use reinterpret_cast<int*>(ptr) to convert a void* to int* safely in C++.

4fill in blank

hard

Fill both blanks to create a map from string lengths to strings, filtering only strings longer than 3 characters.

C++

std::map<int, std::string> length_map;
for (const auto& word : words) {
    if (word.[1] > 3) {
        length_map[static_cast<int>(word.[2])] = word;
    }
}

Drag options to blanks, or click blank then click option'

Aword.length()

Bsize()

Clength()

Dword.size()

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect member functions or missing static_cast for int conversion.

Using word.length() inconsistently.

Use word.size() to get the length and length() to compare string length in C++.

5fill in blank

hard

Fill all three blanks to create a vector of floats from a vector of ints by casting each element.

C++

std::vector<int> nums = {1, 2, 3, 4};
std::vector<float> floats;
for (auto [1] : nums) {
    floats.push_back([2]);
}

float first = floats[[3]];

Drag options to blanks, or click blank then click option'

Anum

Bstatic_cast<float>(num)

C0

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong loop variable name.

Forgetting to cast inside push_back.

Using wrong index to access vector element.

Use num as the loop variable, cast it with static_cast<float>(num), and access the first element with index 0.

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