Programming Concepts & Python — Mock Test 1

len() returns the number of items in a sequence; for a string that is the number of characters — len('HTET') is 4.

Object-oriented programming builds programs around objects, which bundle data with the methods that act on it. Procedural and structured programming are organised around functions.

Abstraction shows only the essential features and hides the details, like driving a car without knowing how the engine works. Encapsulation is wrapping data and methods together in one unit.

A dictionary stores key–value pairs and finds a value through its associated key (d['name']), not by index position as in a list. Dictionaries are therefore called associative arrays.

== compares values (equality), so it is True when two different objects have the same content: [1, 2] == [1, 2]. Testing whether two names are aliases for the same object is the job of 'is'. (== is also True for aliases, but the expected answer separates the two operators.)

A data type specifies the set of legal values a variable can hold (and the operations allowed on them) — e.g. int, float, char.

The membership operators 'in' and 'not in' test whether an element is in a sequence: 3 in [1, 2, 3] gives True.

A tuple is an ordered sequence like a list but immutable: (1, 2, 3) cannot be changed after it is created. A list [1, 2, 3] is mutable.

An algorithm is a finite, step-by-step set of rules for solving a problem or doing a calculation, whether by hand or by machine.

A recursive procedure calls itself with a smaller input until it reaches a base case: factorial(n) = n × factorial(n − 1), with factorial(0) = 1.

A class with at least one pure virtual function (virtual void f() = 0;) is an abstract class; it cannot be instantiated.

A tuple cannot be changed after it is created — it is immutable. Lists are mutable.

A Python list is written in square brackets: [1, 2, 3]. ( ) makes a tuple and { } a set or dictionary.

A flowchart is the pictorial (diagram) form of an algorithm; pseudocode is its text form.

In a dictionary each pair is key: value, e.g. {'a': 1, 'b': 2}.

Instance methods receive the object itself as the first parameter, named self by convention.

An algorithm is a finite, step-by-step procedure for solving a problem.

The py_compile module compiles a .py source file to byte code (.pyc): python -m py_compile file.py.

The Python Virtual Machine (PVM) is the interpreter that runs the compiled byte code.

C++ has copy, conversion and overloaded constructors, but a constructor can never be virtual (the object's type is not yet known while it is being built). Only destructors can be virtual.

stack, queue and priority_queue are container adaptors (derived containers) built on other containers. deque is a basic sequence container.

A unary operator overloaded as a member function takes no argument — the operand is the calling object (this). As a friend function it would take one.

A do-while loop runs its body once before testing the condition. while(0) is false, so "save trees" prints exactly once.

private → visibility specifier, sizeof → operator, static → storage class, long → data type modifier: i-b, ii-c, iii-d, iv-a.

All three are standard rules: a virtual function must be a member of some class, it cannot be a static member, and it can be declared a friend of another class.