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Programming Languages > Lecture 1 > Flashcards

Lecture 1 Flashcards

1
Q

Why are different programming languages written?

A

To solve different problems. Different tools for different reasons.

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2
Q

What are some general purpose languages?

A

C++, C

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3
Q

What are the characteristics of abstraction?

A
  1. Encapsulation

2. Information Hiding

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4
Q

What are the types of abstraction?

A
  1. Data

2. Procedural

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5
Q

What does an optimizer do?

A

Places statements pertaining to the same data close to one another in memory.

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6
Q

What are the three language constructs?

A

Repetition, sequence, condition

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7
Q

What percentage of a company’s budget is spent on maintenance vs. on development?

A

80 % on maintenance.

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8
Q

What is a unit of work?

A

Do the entire unit of work or do nothing. Ex: ATM. Attempts transaction and backs everything out if there is an issue.

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9
Q

What is aliasing?

A

Referring to memory addresses using different types and different symbolic names

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10
Q

What is perfective maintenance?

A

Enhancements

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11
Q

What is protective maintenance?

A

Security

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12
Q

What is adaptive maintenance?

A

Changing technology without changing functionality

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13
Q

What is corrective maintenance?

A

Fixing bugs

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14
Q

Why is compiling programs a cost?

A

Separation of duties. You have individual employees dealing with the build process.

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15
Q

What is reliability?

A

Conformance to specifications

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16
Q

What does overall simplicity mean?

A

A manageable set of features and constructs, minimal feature multiplicity, minimal operator overloading

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17
Q

What is orthogonality?

A

A relatively small set of primitive constructs can be combined in a relatively small number of ways. Optimally, every possible combination is legal.

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18
Q

What is abstraction?

A

The ability to define and use complex structures or operations in ways that allow details to be ignored.

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19
Q

What is expressivity?

A

The breadth of ideas that can be represented and communicated in the language.

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20
Q

What is portability?

A

The ease with which programs can be moved from one implementation to another.

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21
Q

What is generality?

A

The applicability to a wide range of applications.

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22
Q

What computer architecture are programming languages developed around?

A

The Von Neumann architecture

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23
Q

When did the Von Neumann architecture come into ues?

A

1940-1950

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24
Q

What are the characteristics of the Von Neumann architecture?

A
  1. Data and programs stored in memory
  2. Memory is separate from CPU
  3. Instructions and data are piped from memory to CPU
  4. Imperative languages match Von Neumann architecture best.
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25
Q

Why do imperative languages match Von Neumann architecture best?

A
  1. Variables model memory cells
  2. Assignment statements model piping
  3. Iteration is efficient
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26
Q

What is the fetch-execute-cycle on Von Neumann architecture computer?

A
  1. Initialize program counter
  2. Repeat forever:
  3. Fetch instruction pointed to by counter
  4. Increment counter
  5. Decode instruction
  6. Execute instruction
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27
Q

What was the programming paradigm in the 1950s/60s?

A

Simple applications, worry about machine efficiency.

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28
Q

What was the program paradigm in the late 60s?

A

People efficiency became important; requiring better readability and control structures.

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29
Q

What was the program paradigm in the late 70s?

A

Went from process oriented to data oriented

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30
Q

What was the programming paradigm in the mid-1980s?

A

Object oriented programming: Data abstraction + inheritance + polymorphism

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31
Q

What are the categories of languages?

A
  1. Imperative
  2. Functional
  3. Logic
  4. Markup/Programming Hybrid
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32
Q

What are imperative languages?

A
  • Variables
  • Assignment statements
  • Iteration
  • Object Oriented Programming
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33
Q

What are functional languages?

A

Primary means of making computations is by applying functions to given parameters

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34
Q

What is object oriented programming?

A

Simplification of data and procedural abstraction and building it into languages.

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35
Q

What is range checking?

A

A compiler feature that will prevent you from referencing an element that is out of range of the defined size of an array.

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36
Q

What are the language design tradeoffs?

A
  1. Reliability vs. cost of execution
  2. Readability vs. writability
  3. Writability (flexibility) vs. reliability
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37
Q

What are the methods of implementation of programming languages?

A
  1. Compilation
  2. Pure interpretation
  3. Hybrid Implementation Systems
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38
Q

What are hybrid implementation systems?

A

A compromise between compilers and pure interpreters. High level language translated to intermediate language that allows easy interpretation.

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39
Q

What is pure interpretation?

A

Where every line is translated one at a time. It uses more memory and is slower than compilation.

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40
Q

What is an example of a hybrid implementation system?

A

Java Bytecode

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41
Q

What are the phases of compilation?

A
  1. Lexical Analysis
  2. Syntax Analysis
  3. Semantics Analysis
  4. Code Generation
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42
Q

What is lexical analysis?

A

A process that converts characters in the source program into lexical units. This is where the symbol table gets created.

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43
Q

What is syntax analysis?

A

Transforms lexical units into parse trees, which represent syntax.

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44
Q

What is semantics analysis?

A

Attempts to understand the intention of the programmer, generates intermediate code.

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45
Q

How many passes are most compilers?

A

2:

  1. Symbol Table (sometimes Syntax)
  2. (sometiems Syntax), Intermediate Code, uses symbol table for code generation
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46
Q

During which phase in the compilation process can optimization be applied?

A

Semantic Analysis

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47
Q

What is a load module?

A

An executable image, the user and system code together

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48
Q

What is linking and loading?

A

The process of collecting system program units and linking them to a user program.

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49
Q

What is an unresolved reference?

A

When the compiler marks in the symbol table when it is unable to find something

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50
Q

What is a linkage editor?

A

Looks in libraries to find reference and updates symbol table with module if found. Otherwise, error out and fail compilation.

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51
Q

What is the Von Neumann bottleneck?

A

The connection speed between a computer’s memory and its processor determines the speed of a computer. Since instructions can be executed faster than the speed of the connection, a bottleneck is created.

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52
Q

What is a way to get around the Von Neumann bottleneck?

A

Use multiple processors

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53
Q

What are the characteristics of Pure Interpretation?

A
  1. No translation (no .exe output)
  2. Easier implementation of programs
  3. Slower execution
  4. Usually requires more space
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54
Q

What are the characteristics of hybrid implementation systems?

A
  1. Mix of interpreted/compiled
  2. High level program translated to intermediate language that allows easy interpretation
  3. Faster than pure interpretation
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55
Q

What are some examples of Hybrid Implementation Systems?

A

Initial implementations of Java, Perl.

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56
Q

What is the Hybrid Implementation Process?

A
  1. Source Program
  2. Lexical Analyzer
  3. Syntax Analyzer
  4. Intermediate code generator
  5. Interpreter
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57
Q

What is the Pure Interpretation Process?

A
  1. Source Program
  2. Interpreter
  3. Results
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58
Q

Where does the descriptor reside?

A

The symbol table

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59
Q

What is a data type?

A

A collection of data objects and a set of predefined operations on those objects

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60
Q

What is a descriptor?

A

A collection of the attributes of a variable

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61
Q

What is an object?

A

An instance of a user-defined (abstract) data type

62
Q

What are primitive data types?

A

Data types not defined in terms of another set of types

63
Q

T/F - Integer is almost always an exact reflection of the hardware so mapping is trivial

A

True

64
Q

What is the IEEE standard for floating point types?

A

754

65
Q

What happens to the sign of the exponent in floating point data types?

A

It is eliminated to save space

66
Q

What are complex data types?

A

Representation of complex numbers where two floats represent the real and imaginary parts

67
Q

What is packing?

A

In terms of CS, storing information using less memory than designated.

68
Q

What are the attributes of the decimal data type?

A
  • Store a fixed number of decimal digits in BCD
  • Adv: Allow a high degree of accuracy
  • Disadv: Has limited range and wastes memory
69
Q

How are boolean types usually implemented?

A

As bytes

70
Q

What are the attributes of the character data type?

A
  • Stored as numeric coding

- Common codings include ASCII, UCS2 and UCS4. Less common EBCDIC.

71
Q

How are strings stored?

A

As sequences of characters

72
Q

What are the design issues to consider about strings?

A

Static vs dynamic, primitive type or special array

73
Q

How are static strings implemented for processing by a language?

A

As a compile time descriptor

74
Q

Do limited dynamic strings need a runtime descriptor?

A

They may in certain cases, C and C++ don’t

75
Q

Do dynamic length strings need a runtime descriptor?

A

Yes

76
Q

What are the components of a static string descriptor?

A

String, Length, Address

77
Q

What are the components of a runtime descriptor for limited dynamic strings?

A

String, Maximum Length, Current Length, Address

78
Q

What is an ordinal type?

A

A type in which the range of possible values can be easily associated with the set of positive integers. Are always discrete.

79
Q

What is the maximum number of subscripts in C++?

A

255

80
Q

What are the reasons arrays moved from static to heap?

A

1 Dynamic arrays became more useful and viable
2 More heap memory available in total
3 Better hardware, so heap access is faster
4 Able to reference by address

81
Q

What are the advantages and disadvantages of range checking?

A

Adv - Reliability. Prevents you from going out of bounds.

Disadv - Performance hit (lots of if statement / branching)

82
Q

When are subscript ranges bound?

A

Compile time, generally

83
Q

When does allocation take place?

A

It depends. Declaration is not executable unless initialization is associated with it.

84
Q

What are two ways you can make rectangular multidimensional arrays jagged?

A

1- Array of arrays

2- Allocate as rectangular, keep track of used cells

85
Q

What is array slicing?

A

Using a referencing mechanism to represent a substructure of an array

86
Q

What is array indexing?

A

Mapping from indices to elements

87
Q

When should allocation be performed?

A

Only when you have to. (lazy allocation)

88
Q

In static array binding, how are subscript ranges bound, and what type of allocation is used?

A

Bound statically, and allocation is static

89
Q

What is the advantage to static subscript binding?

A

More efficient - no indirect addressing.

90
Q

In fixed stack-dynamic array binding, how are subscript ranges bound, and what type of allocation is used?

A

Bound statically, allocation done at declaration time (dynamic)

91
Q

What is the advantage to fixed stack-dynamic subscript binding?

A

Space efficiency

92
Q

In fixed heap-dynamic array binding, how are subscript ranges bound, and what type of allocation is used?

A

Bound when requested, dynamic but fixed after allocation, allocated from heap.

93
Q

In heap-dynamic array binding, how are subscript ranges bound, and what type of allocation is used?

A

Bound dynamically, allocation is dynamic, can change any number of times.

94
Q

What is the advantage to fixed stack-dynamic subscript binding?

A

Flexibility (grow or shrink during program execution)

95
Q

How does C/C++ treat arrays declared with static modifier?

A

Makes them static

96
Q

How does C/C++ treat arrays declared without static modifier?

A

Makes them fixed stack-dynamic

97
Q

What type of array other than static and fixed stack-dynamic do C/C++ provide?

A

Fixed heap-dynamic

98
Q

How are heterogeneous arrays implemented?

A

By making every element the same size

99
Q

What is happening behind the scenes when you declare an array of strings?

A

It is declaring an array of addresses that point to strongs

100
Q

What is the base address of an array?

A

The address that refers to the first element.

101
Q

How is data accessed in an array behind the scenes?

A

An access function maps subscript expressions to an address in the array.

102
Q

Is row major order or column major order more commonly used to access array elements/

A

Row Major

103
Q

How does a compiler/interpreter tell the computer to access a specific array element?

A

Offset calculations are used, typically taking into account subscript, row and column lower bound, number of elements and element size

104
Q

What are the elements of a compile-time descriptor for a single dimensioned array?

A 
1 Element Type
2 Index Type
3 Index lower bound
4 Index upper bound
5 Address
105
Q

What are the elements of a compile-time descriptor for a multidimensional array?

A 
1 Element Type
2 Index Type
3 Number of Dimensions
4 Index range 1
5 Index range n
6 Address
106
Q

What is an associative array?

A

An unordered collection of data elements indexed by keys

107
Q

Why is hashing more useful than associative arrays?

A

Associate arrays require extra steps due to indirect processing

108
Q

What is a record?

A

A potentially heterogeneous aggregate of data elements in which the individual elements are identified by names

109
Q

What is a good analogy for records?

A

Structure

110
Q

When are records used instead of an array?

A

When data is heterogeneous

111
Q

Is access to array elements faster than record fields? Why or why not?

A

No, because subscripts are dynamic and field names are static.

112
Q

How are records spaced out in memory?

A

An offset address relative to the beginning of the records is associated with each field

113
Q

Where are record layouts stored?

A

In the symbol table

114
Q

What is a union?

A

A type whose variables are allowed to store different type values at different times during execution

115
Q

Can union type checking be performed by a compiler? An interpreter?

A

No.

Yes.

116
Q

In what language are unions safe?

A

Ada

117
Q

In what languages are unions unsafe?

A

Almost all except Ada

118
Q

What is a set?

A

Unordered collections of distinct values of an ordinal type

119
Q

How are sets stored?

A

As bit strings

120
Q

How are set operations defined?

A

Usually as logical operations

121
Q

How do arrays compare to sets?

A

They are more flexible but slower.

122
Q

What values can pointers contain?

A

Memory addresses, and nil

123
Q

What are reference types?

A

A special kind of pointer type used primarily for formal parameters

124
Q

What are examples of heap management algorithms?

A

First fit, best fit, largest fit (worst fit)

125
Q

What is BNF?

A

Backus-Naur form, a formal description of the syntax of source language

126
Q

What are the two components in syntax analysis?

A
  1. Lexical Analyzer

2. Syntax Analyzer (Parser)

127
Q

What is a lexical analyzer, mathematically?

A

A finite automaton based on a regular grammar

128
Q

What is a syntax analyzer, mathematically?

A

A push down automaton based on a context free grammar (BNF)

129
Q

How do compilers and intepreters display syntax errors differently?

A

Compilers show all syntax errors at once, while interpreters show syntax errors one at a time

130
Q

Why is BNF used for parsers?

A

It usually results in easy translation back and forth between the BNF and parse tree.

131
Q

Why is lexical and syntax analysis often separated?

A

Simplicity - Enables simplification of the parser
Efficiency - Enables optimization of the lexical analyzer
Portability - Parser always portable, parts of lexer may not be

132
Q

Why is the parser always portable?

A

Because it is just matching lexed input up to a parse tree.

133
Q

What are lexemes?

A

Substrings of a source program that belong together. They match a character pattern and fit into a lexical category called a token.

134
Q

How do a parser and lexer fit together functionally?

A

The lexer generates strings, identifies tokens of lexemes and passes information to parser.

135
Q

How is a lexical analyzer usually implemented?

A

As a function called by the parser when it needs the next token

136
Q

What are the three approaches to building a lexer?

A
  1. Write formal description of tokens and use software tool to create a table-driven lexer from description
  2. Design state diagram that describes tokens and write program that implements state diagram
  3. Design state diagram that describes tokens and hard-construct a table implementation of state diagram
137
Q

What are the goals of the parser?

A
  1. Find syntax errors, output error message, recover quickly

2. Produce parse tree or trace of parse tree

138
Q

What does a top down parser do?

A

Produces parse tree beginning at root. Uses leftmost derivation & builds tree in preorder.

139
Q

What does a bottom up parser do?

A

Produces parse tree beginning at leaves, uses reverse of rightmost derivation.

140
Q

How does recursive descent parsing work?

A

There is a subprogram for each NT in grammar, which can parse sentences generated by NT.

141
Q

Why is EBNF ideally suited for being basis for an RD parser?

A

EBNF minimizes number of nonterminals.

142
Q

What is coding process when only one RHS?

A

1 For each terminal symbol, compare to next input token. Continue if match, else error.
2 For each nonterminal call associated parsing subprogram

143
Q

How is the correct RHS chosen?

A

On basis of the next token of input (lookahead)

144
Q

What are the phases of a hybrid implementation process?

A 
1 Source
2 Lexer
3 Parser
4 Intermediate code gen
5 Interpreter
145
Q

How does just in time work?

A
  1. Translate programs into intermediate language
  2. Compile intermediate language into machine code WHEN PROGRAMS ARE CALLED
    3 Machine code version kept for subsequent calls
146
Q

What does a preprocessor do?

A

Processes a program immediately before program is compiled to expand embedded preprocessor macros. Allows you to embed code from one language inside another.

147
Q

What language was the basis for most current commonly used programming languages?

A

FORTRAN

148
Q

What are the issues with using machine code to program?

A

1 Poor readability
2 Poor modifiability
3 Tedious coding
4 Machine deficiencies (indexing/ floating point)

149
Q

What language led to the idea of compiled programming languages?

A

FORTRAN

150
Q

When is a grammar ambiguous?

A

When two parse trees can be produced from the same input. It occurs when a rule has the same nonterminal multiple times in the same RHS.

151
Q

What is the difference between a keyword and a reserved word?

A

A keyword is only special in certain contexts. A reserved word is always special and cannot be used in user-defined names. It is a subset of keyword.

Programming Languages (3 decks)

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