Variable declaration and initialization in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of uninitialized local variable

What is the output of this C++ code?

C++

#include <iostream>
int main() {
    int x;
    std::cout << x << std::endl;
    return 0;
}

A Garbage value (undefined behavior)

B 1

C Compilation error

D 0

💡 Hint

Local variables without initialization contain whatever was in memory before.

Local variables in C++ are not automatically initialized. Printing an uninitialized int gives an unpredictable value (garbage).

❓ Predict Output

intermediate

Value of initialized variable with brace syntax

What is the output of this code snippet?

C++

#include <iostream>
int main() {
    int a{5};
    std::cout << a << std::endl;
    return 0;
}

A 0

B 5

C Compilation error

D Garbage value

💡 Hint

Brace initialization sets the variable to the given value.

Using brace initialization int a{5}; sets a to 5.

❓ Predict Output

advanced

Output of const variable initialization

What will this program print?

C++

#include <iostream>
int main() {
    const int x = 10;
    // x = 20; // Uncommenting this line causes error
    std::cout << x << std::endl;
    return 0;
}

A Compilation error

B 20

C Undefined behavior

D 10

💡 Hint

Const variables cannot be changed after initialization.

The const int x is initialized to 10 and cannot be changed. The program prints 10.

❓ Predict Output

advanced

Output of auto type deduction with initialization

What is the output of this code?

C++

#include <iostream>
#include <typeinfo>
int main() {
    auto val = 3.14;
    std::cout << typeid(val).name() << std::endl;
    return 0;
}

A f

B i

C d

D c

💡 Hint

auto deduces the type from the initializer.

auto val = 3.14; deduces val as double. typeid(val).name() returns 'd' for double on most compilers.

🧠 Conceptual

expert

Behavior of static variable initialization

Consider this code snippet. What is the output after running main() twice?

#include 
void func() {
    static int count = 0;
    count++;
    std::cout << count << std::endl;
}

int main() {
    func();
    func();
    return 0;
}

A 1 2

B 0 1

C 1 1

D 2 3

💡 Hint

Static variables keep their value between function calls.

The static variable count starts at 0, increments each call. First call prints 1, second prints 2.