Programming Languages and Compilers

PL/I uses the DO loop construct for iteration control. The correct syntax for repeating an instruction 5 times is DO J=1 TO 5; instruction; END; which creates a controlled loop with an index variable. The REPEAT keyword doesn't exist in PL/I, and the WHILE option would require different initialization and would execute only 4 times with < 5 condition.

In PL/I, semicolons terminate statements rather than acting as separators. Thus, a semicolon is required at the end of each statement (instruction), to terminate groups like DO, and to terminate the program block. However, the options listed are slightly confusing as a DO instruction ends with a separate END statement, which contains a semicolon, but 'at the end of each instruction', 'at the end of the program', and 'to end an IF instruction' (which is terminated by a semicolon) align with PL/I statement terminator rules.

The exit() function is part of the C Standard Library, specifically in the cstdlib header (stdlib.h in C). It's used to terminate program execution and return a status code to the operating system. This is a standard function used throughout C and C++ programs for controlled program termination.

A variable can be declared both const and volatile. This is useful for hardware registers that can change externally (volatile) but shouldn't be modified through the program (const). Example: volatile const int *ptr for memory-mapped I/O.

COBOL and PASCAL are both high-level programming languages, not computer viruses. COBOL (Common Business-Oriented Language) is used in business and finance applications, while PASCAL was designed for teaching programming concepts. Viruses are malicious software that replicate themselves, which these languages are not.

The ref function returns a true value (indicating the reference type) only if its argument is a reference. Since $val holds a plain string ('x') and not a reference, ref returns an empty string (empty value).

Calling B->new() inherits new from package A. In A::new, the single-argument bless {} blesses the object into the current package (A). Thus, \$obj is an instance of A, and \$obj->foo() calls A::foo which returns 'A'.

The code fails because init() is called before bless() returns a fully constructed object. When init() attempts $self->{key} = 'value', $self is still an unblessed hash reference (not yet an object of class A), but more critically, calling init() inside new() before the bless completes means $self lacks proper object context. Perl's bless() operation must complete before the object can properly call its own methods. The correct pattern is to bless first, then initialize, or use a post-bless initialization hook.

The array @a contains (1, undef, 2). The loop iterates three times: first val=1, foo(1) returns 2, sum becomes 2; second val=undef, foo(undef) dies with error message, eval catches it ($@ is true), so sum += 100 making sum = 102; third val=2, foo(2) returns 4, sum becomes 106. The print outputs 106. The eval block traps the die() on undefined input, adding 100 instead of failing.

When Perl evaluates exists $var->{key1}->{key2}, it autovivifies (auto-creates) the intermediate hash structure even though the key2 doesn't exist. This means $var->{key1} is created as an empty hash. The exists check returns false (key2 doesn't exist), so the assignment inside the if block doesn't execute. However, the autovivication already happened, leaving $var with one key (key1). keys(%{$var}) returns 1.

BEGIN blocks execute at compile time in declaration order, while END blocks execute at runtime in reverse declaration order (LIFO - last in, first out). The two BEGIN blocks print 'a' then 'c'. The two END blocks are declared in order (prints 'b' then 'd'), but execute in reverse order, so 'd' prints before 'b'. Final output: 'ac' from BEGIN blocks, then 'db' from END blocks, yielding 'cadb'.

The statement assigns a list to a list, evaluating the right-hand side in list context. The array elements are copied, and since the left-hand side lists only one variable ($b) inside parentheses, it receives the first element of the array, which is 0.

In COBOL Procedure Division, only Sections are optional. You must have at least one Paragraph, which contains Sentences, which are composed of Statements. This hierarchy is: Sections (optional) > Paragraphs (required) > Sentences (required) > Statements (required). A procedure can consist of a single paragraph with sentences, without any sections, making sections the only truly optional element.

In COBOL, START, REWRITE, and DELETE are valid input/output verbs used to perform operations on files. UPDATE is not a valid COBOL verb; modifying an existing record is accomplished using the REWRITE verb. Thus, option D is the correct choice.

Math.random() returns a value in the range [0, 1). Multiplying it by the range size (high - low), rounding the result using Math.round(), and shifting it by adding low correctly generates a random integer in the closed interval [low, high]. Other choices fail to scale or shift the output correctly.