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Problem 1. Basic knowledge

1. Read the following code. Which of the following statements is/are true?

#include <iostream>

int main() {
    std::string s1 = "Hello";
    std::string s2 = "C++";
    std::string s3 = s1 + s2;
    s1 += s2;
    std::cout << (s1 == s3) << std::endl;
}

{{ multiselect(1) }}

• s1 and s3 will have the same content after execution.
• s1 += s2 is equivalent to s1 = s1 + s2.
• The program will output 1.
• s2 is modified during the concatenation operation.

2. Read the following code. Which of the following statements is/are true?

#include <vector>

int main() {
    std::vector<int> v1(5, 10);
    std::vector<int> v2 = {10, 10, 10, 10, 10};
    std::vector<int> v3;
    v3.resize(5, 10);
}

{{ multiselect(2) }}

• v1, v2, and v3 all contain exactly 5 elements with value 10.
• v2 and v3 may have capacities larger than v2.size() * sizeof(int) after initialization.
• The type of v1 is std::vector<int> while v2 is not.
• v3.resize(5, 10) can be replaced with v3 = std::vector<int>(5, 10) for the same result.
• All three vectors use heap memory to store their elements.

3. Read the following code and select the correct statements:

class Counter {  
    int count = 0;  
public:  
    Counter& increment() {  
        ++count;  
        return *this;  
    }  
    Counter reset() {  
        count = 0;  
        return *this;  
    }  
    int getValue() const {  
        return count;  
    }  
    void setValue(int newVal) {  
        this->count = newVal;
    }  
};  

int main() {  
    Counter c;  
    c.increment().increment().reset();  
    c.setValue(5);  
    const Counter& cref = c;  
    int val = cref.getValue(); // Line B  
}  

{{ multiselect(3) }}

• In the increment member function, this is of type Counter*.
• The expression c.increment().increment() is valid and c.count will increase by 2.
• In setValue(int newVal) function, this->count is equivalent to writing count directly.
• Line B will cause a compile error because getValue() is not declared const.
• The reset() function allows chaining calls like c.reset().increment() and c.count will equals to 1 in the end.
• In a const member function (e.g., getValue), this is of type const Counter*.

4. Which of the following statements about references in C++ is/are true?

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• A reference must be initialized when declared.
• References can be rebound to different objects after initialization.
• A function returning a reference to a local variable is safe.
• const int& r = 5; is valid in C++ because r is declared as const.
• References cannot be used as return types for functions.

5. Read the following code. Which of the following statements is/are true?

class Rectangle {
    int width, height;
public:
    Rectangle(int w, int h) : width(w), height(h) {}
    int area() const { return width * height; }
    void setWidth(int w) { width = w; }
};

int main() {
    const Rectangle r(4, 5);
    std::cout << r.area() << std::endl;
    r.setWidth(10);
}

{{ multiselect(5) }}

• The code will compile and output 20.
• r.setWidth(10) will cause a compile error.
• Removing const from r's declaration would fix all compilation issues.
• area() must be declared const to be called on a const object.
• The constructor initializes width before height.

6. Which of the following statements about std::string is/are true?

{{ multiselect(6) }}

• std::string::size() returns the number of characters excluding the null terminator.
• std::strings can be compared using relational operators like <.
• std::string s; initializes s to an empty string.
• We cannot modify the content of std::string once we have initialized the varible.
• std::getline(std::cin, s) stops reading at the first whitespace character.

7. Consider the following code. Which statements about constructors are true?

class Book {
    std::string title;
    int pages;
public:
    Book() : pages(0) {}
    Book(std::string t) : title(t), pages(0) {}
    Book(std::string t, int p) : title(t), pages(p) {}
};

{{ multiselect(7) }}

• Book b; is valid and initializes pages to 0.
• Book b("C++ Primer"); will initialize pages to 0.
• Book b("Effective C++", 500); uses the third constructor.
• The class has a compiler-generated default constructor.
• title is initialized before pages in all constructors.

8. Which of the following code snippets correctly uses range-based for loops?

{{ multiselect(8) }}

• std::vector<int> v{1,2,3};
  for (int i : v) { ... }
  

• int arr[3] = {4,5,6};
  for (auto& x : arr) { ... }
  

• std::string s = "hello";
  for (char c : s) { ... }
  

• const std::vector<float> vec;
  for (float f : vec) { ... }
  

9. Which statements about const member functions are correct?

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• const member functions cannot modify any member variables.
• const member functions can call non-const member functions.
• Non-const objects cannot call const member functions.
• const member functions can return const references to member variables.
• A const pointer to a class can only call const member functions.