12th Standard Computer Science: Previous Year Mixed Test

Explanation. An impure function may change its arguments or other outside state, i.e. it causes side effects; a pure function has no side effects.

Explanation. A concrete data type is one whose representation (implementation) is known; an abstract data type hides its representation.

Explanation. Public members can be accessed from anywhere, including outside the class; private and protected members are restricted.

Explanation. The efficiency of an algorithm is measured by its time complexity and space complexity.

Explanation. In Python IDLE, a script is run using Run > Run Module or the F5 key.

Explanation. 52 % 2 is 0, so the condition is true and the conditional expression assigns "even" to x, which is printed.

Explanation. A function that calls itself is a recursive function (recursion).

Explanation. In Python the + operator joins (concatenates) two strings; * repeats a string.

Explanation. append() adds the element at the end of the list, giving [10, 20, 30, 40, 35].

Explanation. In Python a variable name prefixed with a double underscore (__num) is treated as private.

Explanation. Edgar Frank Codd proposed the relational model of data in 1970 and is called the father of relational database.

Explanation. ALTER TABLE is a DDL command used to add, modify or drop columns, i.e. to change the table structure.

Explanation. CRLF stands for Carriage Return and Line Feed, the line terminator used in CSV files.

Explanation. Boost (Boost.Python) is the C++ framework for interfacing Python and C++; Ctypes, SWIG and Cython are other interfacing tools.

Explanation. The SQL aggregate function MAX() returns the largest value in the selected column.

Explanation. A definition is a distinct syntactic block: it binds a name to a function or value and is written as a separate block of code.

Explanation. Constructors are functions that build (create) an abstract data type; selectors retrieve information from it.

Explanation. Python searches scopes in the LEGB order: Local, Enclosed, Global, Built-in.

Explanation. Binary search repeatedly halves the search interval of a sorted list, so it is also called half-interval search.

Explanation. The ternary operator (x if condition else y) chooses a value based on a condition, so it is called the conditional operator.

Explanation. A for loop runs over a known range or sequence, so the number of iterations is fixed in advance; hence it is a definite loop.

Explanation. The return statement ends the execution of a function and sends control (and optionally a value) back to the caller.

Explanation. A string subscript can be a positive index (from 0, left to right) or a negative index (from -1, right to left). Options (a) and (c) mean nearly the same; the textbook answer is (a).

Explanation. The slice [::-1] uses step -1, so it returns the whole string in reverse order: "ecneicS retupmoC".

Explanation. Class members are accessed with the dot operator, for example object.member.

Explanation. The Entity-Relationship (ER) model was developed by Peter Chen in 1976; E F Codd proposed the relational model.

Explanation. A query that retrieves data from tables is written with the SELECT command; ORDER BY is only a clause of SELECT, and ALTER changes the table structure.

Explanation. Opening an existing CSV file in append mode ("a") and adding more data to it is called appending.

Explanation. The OS module provides functions to interact with the operating system, such as os.system() to run the compiler and the executable.

Explanation. The DISTINCT keyword used with SELECT removes duplicate rows from the result.

Explanation. Big O notation gives the upper bound of an algorithm's running time, so it describes the worst case.

Explanation. An abstract datatype (ADT) shows only what operations can be done; its internal representation is hidden. A concrete datatype has a known representation.

Explanation. In Python IDLE, a script is run using Run > Run Module or by pressing the F5 key.

Explanation. An interface is the set of actions that an object can do; the implementation carries out those actions.

Explanation. Access control is the security technique that decides who can view or use resources in a computing environment.

Explanation. Square brackets [ ] are the slicing operator, e.g. s[0:3] gives a substring.

Explanation. Creating an object (instance) of a class is called instantiation.

Explanation. The condition must use the comparison operator ==; = is assignment and gives a syntax error. A leap year is divisible by 4, so x%4==0.

Explanation. In relational algebra, SELECT is denoted by σ (sigma); PROJECT uses Π and Cartesian product uses X.

Explanation. Indexing starts at 0, so List[2] is 30; assigning 35 replaces it, giving [10, 20, 35, 40, 50].

Explanation. A CSV file stores tabular data as plain text records, so it is also called a flat file.

Explanation. The SELECT statement, used to retrieve data from tables, is the most commonly used SQL statement.

Explanation. x takes values 0 to 4. When x is 2, continue skips the print, so the output is 0 1 3 4.

Explanation. A dashboard gathers several resources such as charts and tables into one unified visual display.

Explanation. ORDER BY sorts the result in ascending or descending order; SQL has no SORT BY clause.

Explanation. In Python, variables defined in a class without a double-underscore prefix are public and can be accessed from outside the class; private members (prefixed with __) cannot be accessed directly.

Explanation. continue, break and while are reserved keywords in Python; "operator" is only the name of a standard library module, not a keyword.

Explanation. Subroutines are small sections of code that perform a particular task and can be used repeatedly in a program.

Explanation. Python has three important control structures: sequential, alternative (branching) and iterative (looping).

Explanation. Class members are accessed using the dot (.) operator, as in object_name.member_name.

Explanation. The hierarchical model stores data in a tree structure where each child record has only one parent, representing a parent-child relationship.

Explanation. In Python the + operator joins two strings, e.g. "Hello" + "World" gives "HelloWorld"; * is used for repetition.

Explanation. Importing a C++ program into a Python program is called wrapping: the C++ code is wrapped so that it can be called from Python.

Explanation. DROP TABLE removes the whole table (structure and data) from the database; DELETE only removes rows and ALTER TABLE changes the structure.

Explanation. The SQL aggregate function MAX() returns the largest value of the selected column; HIGH(), MAXIMUM() and LARGE() are not SQL functions.

Explanation. A concrete data type is one whose representation (implementation) is known; an abstract data type hides its representation.

Explanation. A function that calls itself is a recursive function, and the process is called recursion.

Explanation. Non-text files such as images or exe files are opened in binary mode (for example "rb" or "wb"), which returns bytes instead of strings.

Explanation. Memoization stores the results of already solved subproblems so they need not be calculated again in dynamic programming.

Explanation. The | operator gives the union of two sets: all elements of both sets without duplicates, so A|B = {1, 3, 6, 9}.

Explanation. Definitions are distinct syntactic blocks; a function definition binds a name to a block of code.

Explanation. Constructors build an abstract data type, while selectors retrieve information (individual values) from it.

Explanation. A namespace is a container that maps variable names to the objects they refer to.

Explanation. The word "algorithm" is derived from the name of the Persian mathematician al-Khowarizmi.

Explanation. Relational operators such as ==, !=, < and > compare two values and return True or False, so they are also called comparative operators.

Explanation. In Python, 'elif' is the short form of 'else if' and is used to check multiple conditions in a chain.

Explanation. A lambda function is defined without a name using the lambda keyword, so it is called an anonymous function.

Explanation. Python strings are immutable, so assigning to str1[7] raises TypeError: 'str' object does not support item assignment.

Explanation. append() adds the element at the end of the list without sorting, giving [17, 23, 41, 10, 32].

Explanation. __del__() is the destructor, called when an object is destroyed; __init__() is the constructor.

Explanation. In a relational table, each row (record) is called a tuple, while each column is an attribute.

Explanation. The ORDER BY clause sorts the result in ascending (ASC) or descending (DESC) order; SQL has no SORT BY clause.

Explanation. CRLF stands for Carriage Return and Line Feed, the line terminator used in CSV files.

Explanation. Boost (Boost.Python) is the C++ library framework for interfacing Python and C++; Ctypes is a foreign function library and Cython is a compiler.

Explanation. SQLite is a lightweight relational database system that stores data in tables and is queried with SQL.

Explanation. Subroutines are small sections of code that perform a particular task and can be used repeatedly in a program.

Explanation. Negative indices count from the end: List[-1] is 10, so List[-2] is 8.

Explanation. SQLite stores data in tables (relations) and is queried with SQL, so it is a relational database system.

Explanation. The word "algorithm" is derived from the name of the Persian mathematician al-Khowarizmi.

Explanation. In Python, a single line comment starts with the hash (#) symbol; everything after it on that line is ignored.

Explanation. Python uses indentation (not braces) to mark blocks of code, so indentation plays a vital role.

Explanation. The return statement ends the execution of a function and sends control (and a value) back to the caller.

Explanation. Python strings are immutable: once created, their characters cannot be changed in place.

Explanation. Constructors are functions that build (create) an abstract data type; selectors retrieve information from it.

Explanation. Creating an object (instance) of a class is called instantiation.

Explanation. DBMS stands for DataBase Management System, the software used to create and manage databases.

Explanation. The ORDER BY clause sorts the result of a query in ascending (ASC) or descending (DESC) order; SQL has no SORT BY clause.

Explanation. The OS module provides functions to interact with the operating system, such as running commands with os.system().

Explanation. Binding a variable name to an object is called mapping; for example, in a = 5 the name a is mapped to the object 5.

Explanation. plot() only draws the data; plt.show() opens the window that displays the plot.

Explanation. A pure function always returns the same result for the same arguments and has no side effects.

Explanation. A tuple is an ordered sequence whose elements cannot be changed after creation, so it is immutable; a list is mutable.

Explanation. Private members are accessible only from within the class; protected members are also available to derived classes and public members everywhere.

Explanation. The efficiency of an algorithm is measured by its time complexity (running time) and space complexity (memory needed).

Explanation. IDLE stands for Integrated Development Learning Environment, the editor and shell supplied with Python.

Explanation. range(2,10,2) starts at 2 and steps by 2 but stops before 10, giving 2, 4, 6, 8.

Explanation. math.floor() returns the largest integer less than or equal to x, so floor(14.4) = 14.

Explanation. Python strings are immutable, so str[3]="-" raises a TypeError and the string stays "NEW DELHI". The question is flawed (the code prints nothing), so the intended answer is taken as the unchanged string.

Explanation. In a dictionary each key is separated from its value by a colon, e.g. {'a': 1}.

Explanation. Class members are accessed with the dot operator, as in object.member.

Explanation. In relational algebra, SELECT is denoted by sigma (σ); PROJECT uses π and Cartesian product uses ×.

Explanation. DROP TABLE removes the whole table with its structure; DELETE removes only rows.

Explanation. A CSV file stores tabular data as plain text records with comma-separated fields, so it is called a flat file.

Explanation. Boost (Boost.Python) is the C++ framework used for interfacing Python and C++; Ctypes is a Python foreign function library, SWIG a wrapper generator and Cython a compiler.

Explanation. A database is an organized collection of related data; a DBMS is the software that manages it.