Programming and data structures

1. What is required for recursion to terminate?

1. A global variable
2. A base case
3. An infinite loop
4. A compiler

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B: A base case. Without a base case, the stack eventually overflows.

2. What is encapsulation in OOP?

1. Using many classes
2. Bundling data and methods together and hiding internal state
3. Copying objects
4. Inheriting from two classes

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B: Bundling data and methods together and hiding internal state. Attributes are accessed through methods rather than directly.

3. What happens when a parameter is passed by reference?

1. A copy is made
2. The original variable can be changed by the subroutine
3. The program crashes
4. It becomes a constant

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B: The original variable can be changed by the subroutine. Passing by value copies the data instead.

4. What is the scope of a local variable?

1. The whole program
2. Only the subroutine where it is declared
3. All subroutines
4. Only global code

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B: Only the subroutine where it is declared. This helps avoid unintended side effects.

5. What does polymorphism allow?

1. Only one class in a program
2. Objects of different classes to be treated through a common interface
3. Faster compilation
4. Direct access to private data

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B: Objects of different classes to be treated through a common interface. Methods can behave differently depending on the object.

6. What is a global variable?

1. A variable used in one subroutine only
2. A variable accessible throughout the entire program
3. A constant
4. A parameter

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B: A variable accessible throughout the entire program. Overuse can cause unintended side effects.

7. What is inheritance in OOP?

1. Copying code manually
2. A class acquiring the attributes and methods of a parent class
3. Hiding data
4. Passing parameters

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B: A class acquiring the attributes and methods of a parent class. It supports reuse and hierarchy.

8. Why is input validation important?

1. It speeds up code
2. It prevents invalid or malicious data causing errors or security issues
3. It reduces file size
4. It removes comments

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B: It prevents invalid or malicious data causing errors or security issues. Defensive design anticipates misuse.

9. A recursive function fact(n) returns n * fact(n-1) and has no base case. What will most likely happen when fact(3) is called?

1. It loops without using any memory
2. It returns 0
3. A stack overflow error occurs
4. It returns 6

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C: A stack overflow error occurs. With no base case the calls never stop. Each call adds a stack frame, so the call stack eventually runs out of space. It does not return 6, because that needs a base case.

10. function f(n): if n == 0 return 0, else return n + f(n-1). What value does f(4) return?

1. 24
2. 4
3. 10
4. 6

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C: 10. f(4) = 4 + 3 + 2 + 1 + f(0) = 10. It is a running sum, not a product, so 24 is wrong.