PLC Fill In Blank

Why are floating point numbers often not associative?

Overflow problem

True or False? An unconditional branch statement, or goto, transfers control to a specified location in a program.

True

True or False? C# allows the control expression and case labels to be strings.

True

True or False? C# includes both the reference of Java and the pointer of C++.

True

True or False? C# users can define their own collections and write their own iterators.

True

True or False? C's for statements often have empty bodies since all the work can be done in the controlling expressions.

True

True or False? C99 can have a declaration in its first expression.

True

True or False? Every counting loop can be built with a logical loop, but the reverse is not true.

True

True or False? In APL, the order of operator evaluation is determined entirely by associativity, which is right to left for all operators.

True

True or False? In C and C++, pointers can point to a function.

True

True or False? In C, the comma operator can be used to join multiple expressions into a single expression.

True

True or False? In Java, unary plus and minus cause the implicit conversion of short and byte operands to int type.

True

True or False? In PHP's switch statement, the case values can be any scalar types.

True

True or False? In PHP, each array contains an internal pointer to its "current" element.

True

True or False? In Python, elements in a list can be of a different type.

True

True or False? In none of Scheme's COND predicates are true, and there is an ELSE statement, it's expression is evaluated and the value is returned?

True

True or False? In the functional languages ML, F# and Lisp, a selector is not a statement; it is an expression that produces a value.

True

True or False? Java and C# allow only Boolean expressions in if statements.

True

True or False? Lists can be nested.

True

True or False? Lists in Python are mutable.

True

True or False? Pointers in C can point to any variable.

True

True or False? Pointers in PL/I can refer to both heap-dynamic variables and other program variables.

True

True or False? Python and ML can include elements of mixed types.

True

True or False? Python's tuples can be empty.

True

True or False? The exit statements in Java and Perl (i.e. break and last) can specify a label.

True

True or False? The expression -count++ is interpreted as -(count++), not (-count)++.

True

True or False? When a Scheme COND expression that follows the predicate is evaluated it is returned as the value of COND.

True

True or false? A reference type in C++ must be initialized at the time it's bound to storage and cannot refer to any other variable during its lifetime.

True

True or false? All variables in Smalltalk, Python, Ruby and Lua store references and are implicitly dereferenced.

True

True or false? An array name not followed by subscripts can be used as a pointer to the first element of the array

True

True or false? Arithmetic cannot be performed on references.

True

True or false? Operators in Ruby can be overridden.

True

True or false? Perl, Python and Lua do not have multiple-selection statements.

True

True or false? The value of an expression may depend on the order of evaluation of the operators in the expression.

True

True or false? When the heap-dynamic variable is deallocated, the tombstone remains.

True, set to nil

True or False? Java supports associative arrays?

True. As a matter of fact, Perl, Python, Ruby, C++, C# and F# do too.

True or False? Visual Basic's exponentiation operator is left associative.

True. Most languages are right associative

In Scheme, when using COND, the predicates are evaluated in order until one evaluates to ____.

#T

What character does a hash in Perl begin with?

%

How do you get the address of a variable in C?

&

Give an example of a multiple-source assignment statement in Perl.

($first, $second, $third) = (20, 40, 60);

Provide an example of using the each statement in Ruby.

>> list = [2, 4, 6, 8] => [2, 4, 6, 8] >> list.each {|value| puts value} 2 4 6 8 => [2, 4, 6, 8]

True or False? In ML, elements of a list can be of different types.

False

True or False? Run-time descriptors of records are necessary.

False

True or false? Multiple exits from a control structure pose a danger.

False

True or false? Narrowing conversions are safe.

False

True or false? Unions in C and C++ are strongly typed?

False

True or false? In Java, floating point division by zero is an error.

False, infinity is a well defined value

True or False? In C#, implicit execution of more than one segment of a switch statement is allowed.

False, only 1

True or false? Java and C# allow mixed-mode assignments if the required coercion is either widening or narrowing.

False, only widening

True or false? Java and C# provide safe unions.

False, unions not included

True or False? In a Scheme list, elements are separated with a comma.

False- no punctuation

True or False? C based languages give OR a higher precedence than AND.

False. AND gets higher precedence than OR

True or false? In pure functional languages, content counters are used for iteration.

False. Do not contain counter variables and recursion is used instead of iteration

True or False? ML's tuples can be empty.

False. Must have at least 2 elements

What are the two ways to reference elements of a record?

Full Qualified Notation and Elliptical Reference

What are associative arrays called in Perl? Why?

Hashes, because elements stored/received with a hash function

In which programming language did list comprehensions first appear?

Haskell

When can a short-circuit expression cause an issue?

If a Boolean expression contains a side-effect, the side-effect may not occur

How does Java take care of the deallocation of heap-dynamic variables?

Implicitly using their garbage collector.

In Object Oriented Programming Languages, records are simulated with ________.

Objects

Name two other ways to implement a multiple selection statement.

binary search and hash table

In Ruby, a _____ is a sequence of code delimited by either braces or the do and end reserved words.

block

The ______ of a loop is the collection of statements whose execution is controlled by an iterative statement.

body

Java's while and do statements are like those of C and C++, except the control expression must have a ______ type.

boolean

Prior to C99, C had no _______ type. Instead, numbers were used.

boolean

What is the best implementation technique of a multiple-selection statement?

branch table (or jump table)

In a loop, what is an example of an unlabeled exit?

break

What is a narrowing conversion?

converts a value to a type that cannot store even approximations of all the values of the original type. i.e. int to byte

In Python, tuples can be deleted with the ____ statement.

del

What is a unary plus operator called? Why?

identity operator Since it usually has no effect

Python includes an _________ tuple type.

immutable

How do you access elements of a tuple in Python?

indexing

In a branch table, the ______ of the table are the case values.

indices

In most programming languages, binary operators are _______, appearing between their operands.

infix

How to prevent coercion in the relational expression In Ruby?

instead of using ==, use eql?

An ______ _______, or loop, causes a statement or collection of statement to be executed zero, one or more times.

iterative statement

In iteration based data structures, an iterative statement uses an _______ to traverse the elements of a data structure.

iterator

An operator can either have ______ or ______ associativity.

left or right

A counter controlled loop has a ______ ________ in which the count is stored.

loop variable

Name one operation in C used for heap allocation.

malloc

Most of the characteristics of arithmetic expressions in programming languages were inherited from ________.

mathematics

The problem of lost heap-dynamic variables is sometimes called ____ ______.

memory leakage

A _____-__________ statement allows the selection of one of any number of statements or statement groups.

multiple-selection

Describe the full qualified notation

must include all record names

How do you create a tuple in Python?

myTuple = (3, 5, 8, 'apple')

Type conversions are either _______ or ________ and can be explicit or implicit.

narrowing/widening

In Java, the else clause is always paired with the _______ previous unpaired then clause.

nearest

In Java, a value of a reference type is like a pointer, except that it must refer to an ______.

object

The ________ associated with a field specifies the distance from the beginning of the record to the beginning of the field.

offset

If pointers can point to variables that are not heap-dynamic, then there must be an _______ or _______ _________ that fetches the address of a variable.

operator or built-in subprogram

What is a mixed-mode conversion?

operators can have operands of different types

In programming languages, arithmetic expressions consist of what?

operators, operands, parentheses and function calls

Unary operators can be either ______ or _______.

pre/post fix

How can pretest logical loops be simulated in a functional language?

recursive function

A program has the property of ______ ______ if any two expressions with the same value can be substituted for each other without affecting the program's behavior.

referential transparency

A _______ ________ compares the values of its two operands.

relational operator

Assignments are ______ associative.

right

A ______ ________ provides a way of choosing between two or more execution paths in a program.

selection statement

List comprehensions are derived from _____ notation.

set

With _______ ________ _________, the value of an expression is determined without evaluating all its subexpressions.

short-circuit evaluation

What is an example of a multiple-selection statement in C#?

switch

What does the current function return in PHP?

the element that is currently being pointed to by the internal pointer

What is a side-effect?

the result when an operator or function call performs some other action in addition to returning a value i.e. int j = ++i + i; What is j? depends on the associativity

What are free unions?

the unions in C and C++ where there is no language support for type checking

Why are tuples used in Python, ML and F#?

to allow function to return multiple values

What's the ternary operator used for?

to form conditional expressions in C based languages

What are the two general paths that selection statements fall into?

two way and n-way

Elliptical references allow leaving out of record names if the reference is _________.

unambiguous

Write an example of a union in C.

union { int I; float f; }u; So you can write: float x; .... u.i = 27; x = u.f;

For a subprogram to use a pointer in C#, you must include the _____ modifier.

unsafe

Instead of a counting loop, Ruby has the _____ method.

upto i.e. >> 1.upto(5) {|x| print x, " "} 1 2 3 4 5

In ML, how are names bound to values?

using val (i.e. val cost = quantity * price;)

C and C++ allow pointers of type ______, which can point at values of any type.

void*

What is the return type of the function malloc?

void*

How to prevent a list from being treated as a function call?

with a quote i.e. (CAR ' (A B C) ) ....returns A

How can you access the first two elements of a tuple in F#?

with the functions fst and snd.

Name one area where pointers are beneficial.

writing device drivers

In C, ______ is considered false.

zero (all other values represent true)

The operator precedence rules of the common language are nearly all the same and include:

- 1. Exponents has the highest precedence - 2. Multiplication and division have lower precedence than 1 - 3. Addition and subtraction have lower precedence than 2.

If the pointer is pointing to an array, what are the 3 forms of pointer arithmetic supported in C and C++?

- Adding an integer to a pointer - Subtracting an integer from a pointer - Subtracting two pointers

What are the two operations that programming languages provide that have pointer types?

- Assignment - Dereferencing

What do the three expression in C's for loop represent?

- First expression: initialization - Second expression: loop control test - Third expression: Often used to increment loop counter since it's evaluated after each execution of the loop body

Name two ways that the following list can be interpreted as: (A B C)

- If interpreted as code, it's a call to the function A with parameters B and C - If interpreted as data, it's a list with 3 elements: A, B and C.

What were pointers designed to do?

- Indirect addressing - Accessing anonymous variables in the heap

What are the three parameters that the counter controlled loop also has?

- Initial value of the loop variable - Terminal value of the loop variable - Step size - the difference between sequential value of the loop variable

What are the two capabilities that most programming languages need?

- Select from among alternative control flow paths - Repeatedly execute sequence of statements

What are the three types of operators

- Unary: one operand - Binary: two operands - Ternary: three operands

What does a list comprehension do?

- applies a function to each element of a list and constructs a new list from the results. - i.e. in Python [x * x for x in range(12) if x % 3 == 0] produces [0, 9, 36, 81]

In C#, the last statement in each selectable segment ends with either a _____ or a _____.

- break - goto

How do you change a tuple in Python?

- by using the list function to convert it to a list - after the change use the tuple function to convert the list back to a tuple

To logically separate code segments in a switch, an _______ _______ much be used; C's _____ statement is an example and exits the switch statement

- explicit branch - break

Name the ML alternatives to CAR and CDR.

- hd (head) i.e. hd [5, 7, 9] is 5 - tl (tail) i.e. tl [5, 7, 9] is [7, 9]

What is the purpose of === operator in PHP?

- the "is identical to" operator prevents type coercion - i.e. "7" == 7 is true but "7" === 7 is false

Name two proposed solutions for the dangling pointer problem.

- the use of tombstones - the use of locks-and-keys

In F#, when an if construct has no else clause, the then clause must return a value of the ____ type. This type has only one value, which is written _________.

- unit - ()

What is a lost heap-dynamic variable?

A dynamic variable that is no longer accessible to a program

What is the locks-and-keys approach?

A pointer is stored as a (key, address) pair where the key is an integer value and each heap-dynamic variable has a header cell that store an integer lock value. When the heap-dynamic variable is allocated, a lock value is created and placed both in the lock cell of the heap-dynamic variable and in the key-cell of the pointer. When the pointer is dereferenced, the key value of the pointer is compared to the lock value of the heap-dynamic variable.

What are discriminant unions?

A union with a discriminant where each union includes a type indicator, knows as a tag or discriminant.

Which language has a single level of precedence?

APL

What is an associative array?

An unordered collection of data elements that are indexed by keys.

What's is Lua's only data structure?

Associative arrays

________ and ________ proved in 1966 that all algorithms could be expressed using only two control statements: one for choosing between two control flow paths and one for logically controlled iteration.

Bohm and Jacopini

What is the value of the relational expression normally?

Boolean

In Perl, subscripting is done using _______ and _______.

Braces and keys

In Scheme and Common Lisp, the ____ function returns the first element of a list.

CAR

In Scheme and Common Lisp, the _____ function returns the list minus its first element.

CDR . i.e. (CDR ' (A B C) ) returns (B C)

Records were introduced in what programming language?

COBOL

What is Scheme's multiple selector called?

COND

What happens when none of the predicates are true and there is no ELSE in Scheme's COND?

COND returns an unspecified value

_______ returns a new list with its first parameter as the first element and its second parameter as the remainder of that list.

CONS i.e. (CONS 'A '(B C)) returns (A B C)

In Java and C#, records can be defined as _______.

Classes

What does -> do?

Combines dereferencing and field reference.

What are reference types mainly used for?

Declaring parameters

What are associative arrays called in Python?

Dictionaries

In Perl, the ________ operator tests whether a value is a key in a hash.

Exists

_______ are the fundamental means of specifying computations in programming languages.

Expressions

How are fields of a record stored in memory?

In adjacent memory locations

In PHP, a subscript can be an ______ or a _______.

Integer or string

What is a dangling pointer?

It's a pointer that contains the address of a heap-dynamic variable that has been deallocated.

Is the following code valid in Ruby and does it produce the result displayed? >> 4.times {puts "Hey!"} Hey! Hey! Hey! Hey! => 4

It's valid and does produce the results displayed

Each element of an associative array is a pair consisting of a _______ and a _______.

Key and value

______ takes any number of parameters and returns a new list with the parameters as the elements.

LIST i.e. (LIST 'A 'B (C D)) returns (A B (C D))

______ ___________ are a powerful mechanism for creating lists.

List comprehensions

______ in Scheme and Common Lisp are enclosed in parentheses.

Lists

What was the first high-level programming language to include pointer variables?

PL/I

How do you override normal precedence and associativity rules?

Parenthesis

In Python, tuples can be catenated with the ______ _________.

Plus operator

_____ type values consist of memory addresses and the special value 'nil'

Pointer

What is a tombstone?

Pointer variables point to a tombstone cell that in turn points to the heap-dynamic variables.

What's the difference between a record and an array?

Record elements (fields) are referenced by name instead of indices.

What's the difference between Ruby's associative arrays and Perl's?

Ruby's keys can be objects. In Perl they can only be strings.

What does the assignment operation do?

Sets a pointer variable's value to some useful address

What does the continue statement do in a loop?

Skips the rest of the loop body

In ML, lists are specified in ______ ________, with the elements separated by ________.

Square brackets, commas

In Perl, each key is a _____ and each value is a _______.

String, scaler

In C, C++ and C#, records are supported with the _______ data type.

Struct

Lua's ______ can be used as records.

Tables

What does the reserved word rec indicate in F#'s function declaration?

That the function is recursive

What happens when an overloaded operator is used in an expression?

The compiler examines the types of operands to determine the correct meaning of the operator

Why are dangling pointers dangerous?

The location being point to may have been reallocated to some new heap-dynamic variable.

What is a difference between Python's dictionaries and Perl's hashes?

The values in Python are references to objects. In Perl they're scalars.

How are record fields accessed in memory?

Through offset

What is the best solution to the dangling pointer problem?

To provide implicit deallocation for heap-dynamic variables that are no longer useful

In Perl, how are elements removed from hashes?

Using delete

When does overflow occur?

When the result of an operation is too large to store in the designated amount of memory

When does underflow occur?

When the result of an operation is too small to represent.

How are new lists constructed in Scheme and Common Lisp?

With CONS and LIST functions.

How do you create a tuple in F#?

With the let statement. i.e. let tup = (3, 5, 7);;

How can tuples be defined in ML?

With the type declaration. i.e. type intReal = int * real;

Does PHP have associative arrays?

Yes

Name two ways to represent an empty list in ML.

[ ] or nil

What is a control structure?

a control statement and the collection of statements whose execution it controls

What is a record?

a data structure in which individual elements are identified by name

What is a tuple?

a data type that's like a record except that elements are not named.

If parentheses are omitted in control expressions, what is normally used?

a keyword marker such as then

What is a posttest loop?

a loop that tests the condition for loop completion after the loop body is executed.

What is a pretest loop?

a loop that tests the condition for loop completion before the loop body is executed.

What is a union?

a type whose variables can store different type values at different times during execution

Which language introduced compound assignment operators?

algol 68

What is a reference in C++?

alias for another variable

If pointers are used only to manage dynamic storage, the pointer variable is initialized by an ___ ___.

allocation mechanism

Describe elliptical references

allow leaving out of record names if the reference is unambiguous

Why does Java coerce byte variables into integers before an arithmetic operation is performed?

architecture. There's a way to add integers together, but not bytes.

How are cases matched in a branch table?

array subscripting

How are arithmetic and relational operators implemented in Ruby?

as methods since Ruby is a purely Object-Oriented language

When an expression contains adjacent occurrences of operators with the same precedence, __________ rules determine which operator is associated first.

associativity

Operator evaluation is governed by __________ and ___________ rules.

associativity and precedence

Why are lost heap-dynamic variables sometimes referred to as garbage?

because they're no longer useful, but the space they occupy cannot be reallocated

Why are casts placed in parentheses?

because type names may consist of more than one word: i.e. long double

How are unions implemented?

by assigning the same address to every possible variant

How does Python specify compound statements?

by using indentation

The ______ ______ _______ combines assignment with some other operation.

compound assignment operator (i.e. sum+=value)

What are the statements that provide the 2 capabilities called?

control statements

What is a widening conversion?

converts a value to a type that can include at least the approximations of all the values of the original type. i.e. int to double

Ruby's multiple-selection constructs are called _____ ________.

case expressions

What are explicit type conversions called?

casts

What are implicit type conversions called?

coercions

Accessing the memory cell a pointer points to is called ________ the pointer.

dereferencing

In a branch table, the _____ of the table are the segment values.

elements

In Ruby, the entire if construct is terminated by the word _____.

end

What is Java's solution to iteration over elements in an array?

enhanced for loop

What is another word for a run-time error?

exception

Languages that provide pointers for heap allocation must include an _____ ______ ________.

explicit allocation operation

Dereferencing can be either _____ or _______.

explicit or implicit

In most programming languages, dereferencing is done _______.

explicitly

How do you dereference a pointer in C++?

explicitly using the (*) as a prefix unary operation. i.e. j = *ptr

In C#, the iterator can be accessed through the _______ statement.

foreach

In Lisp, operators are _______.

functions

What's another term for lost-heap dynamic variables?

garbage

What is the unconditional branch statement called?

goto

If a pointer points to a structure in either C or C++, how can you access a field named age?

i.e. (*p).age or p->age