CS4337 - Final
What are the advantages of named constants?
Readability Used to parameterize programs
A C++ switch allows more than one case to be executed. True False
True
A nested if is one way to implement a multiple-way selection statement. True False
True
What is the output of the following Python code? x = 3 y = 4 z = 5 x,y,z = y,z,x y,x,z = y,z,z x,x,y = z,y,x print x,y,z a. error b. 3 3 4 c. 5 3 4 d. 3 3 3 e. 4 3 5 f. 5 3 3
f. 5 3 3
Variables that are defined inside subprograms are called " _______ variables".
local
If the "then" reserved word or some other syntactic marker is not used to introduce the 'then' clause, the control expression is placed in ______.
parentheses
In functional programming languages, loops are implemented using ______.
recursion
Why are named constants used, rather than numbers, for token codes?
"Although tokens are usually represented as integer values, for the sake of readability of lexical and syntax analyzers, they are often referenced through constants" p. 170
Compute the weakest precondition for each of the following sequences of assignment statements and their postconditions: a) a = 2 * b + 1; b = a - 3 {b < 0} b) a = 3 * (2 * b + a); b = 2 * a - 1 {b > 5}
(a) a - 3 < 0 a < 3 (precondition for second assignment) 2b + 1 < 3 2b < 2 b < 1 (answer) b) 2a - 1 > 5 2a > 6 a > 3 (precondition for second assignment) 3 (2b + a) > 3 2b + a > 1 2b > 1 - a b > 1/2 - a/2 (answer)
Chapter 3
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Chapter 5
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Chapter 6
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Chapter 7
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Chapter 8
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Chapter 4
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What are the two distinct goals of syntax analysis?
1. Make sure that the program is syntactically correct; the compiler must find as many errors as possible in the code. When an error is found, a message is displayed and the compiler returns to a normal state and continues analyzing the code displaying even more errors if there are any. 2. Produce a complete parse tree or a trace of the structure that is used as the basis for translation. The tree is made for syntactically correct input. (p.178)
Briefly describe three advantages of LR parsers.
1. They can be built for all programming languages 2. Syntax errors can be detected as soon as it is possible in left-to-right scan 3. The LR class of grammars is a proper superset of the class parsable by LL parsers, meaning that many left-recursive grammars are LR, but none of these left recursive grammars are LL.
Write EBNF descriptions (i.e. rules) for the a Java class definition header statement. Begin with the start symbol <class_header>. Use the non-terminal <class_name> for the user-defined name of the class. You do not have to include a LHS rule which defines valid naming conventions to expand the <class_name> non-terminal.
<class_head> → {<modifier>} class <class_name> [extends class_name [implements <interface_name> {, <interface_name>}] <modifier> → public | abstract | final
In C-family for loop syntax, match the elements to their description. for ( A ; B ; C ) D A B C D A. Statement(s) to be executed B. Initial value C. Step size value D. Terminal value
A - B. Initial value B - D. Terminal value C - C. Step size value D - A. Statement(s) to be executed
Using the algorithm described in Section 4.4.2, remove direct left recursion form the following grammar rules. A → Aa | Abc | bc | d
A = A, α _1 = a, α_2 = bc, β_1 = bc, β_2 = d A -> bcA' | dA' A' -> aA' | bcA' | Ɛ
Define static binding and dynamic binding.
A binding is static if it first occurs before run time and remains unchanged throughout program execution A binding is dynamic if it first occurs during execution of the program
What is a block?
A method of creating static scopes inside program units
Match these Storage Binding and Lifetime categories of scalar variables with their definitions. Variables that are bound to memory cells before program execution begins and remain bound to those same memory cells until program execution terminates. Variables that are nameless (abstract) memory cells allocated and deallocated by explicit run-time instructions written by the programmer. Variables whose storage bindings are created when their declaration statements are elaborated, but whose types are statically bound. Variables bound to heap storage only when they are assigned values. OPTIONS A. Static variables B. Stack-dynamic variables C. Explicit heap-dynamic variables D. Implicit heap-dynamic variables
A, C, B, D
Match the terms with their definitions. The process of taking a memory cell from a pool of available memory and binding it to a variable. The time during which the variable is bound to a specific memory location. The process of placing a memory cell that has been unbound from a variable back into the pool of available memory. The binding of more than one variable to the same memory cell. OPTIONS A. Allocation B. Deallocation C. Lifetime D. Aliasing
A, C, B, D in order
What are the advantages and disadvantages of dynamic scoping?
Advantages: Convenience Disadvantage: 1. While a subprogram is executing, its variables are visible to all subprograms it calls 2. Impossible to statically type check 3. Poor readability - it is not possible to statically determine the type of a variable
Show a complete parse, including the parse stack contents, input string, and action for the string (id + id) * id, using the grammar and parse table in Section 4.5.3.
Again, NOTES.
Describe, in English, the language defined by the following grammar: S → ABC A → aA | a B → bB | b C → cC | c
All strings that contain one or more a's followed by one or more b's followed by one or more c's. The following strings are all in the language: abc abbbbbbbbbbc aaaaaaaaaabbcc aabcc
What are the design issues for names?
Case sensitivity Whether special words are reserved words or keywords Special characters Length limit
Show a complete parse, including the parse stack contents, input string, and action for the string id * (id + id), using the grammar and parse table in Section 4.5.3.
Check your notes. RIGHT NOW.
Match the term to the definition. Variable Keyword Reserved word Name OPTIONS A. A word of a programming language that is special only in certain contexts. B. A special word of a programming language that can- not be used as a name. C. A string of characters used to identify some entity in a program. D. An abstraction of a computer memory cell or collection of cells.
D, A, B, C
What is a static ancestor of a subprogram? What is a dynamic ancestor of a subprogram?
Enclosing static scopes (to a specific scope) are called its static ancestors Dynamic ancestors are those that are called to reach the subprogram in question
In programming languages, the use of keywords is more restrictive than reversed words. (T/F)
F
Like the if/else statement in Java and C++, the Racket else statement is optional. (T/F)
F
Python data types are declared explicitly. (T/F)
F
A C# switch allows more than one case to be executed. True False
False
In Racket, a "cond" control statement requires an else option. True False
False
In Racket, a "when" control statement permits an else option.
False
What is the boolean evaluation of the following expressions in PHP? (Note: triple equal sign operator) 2 === 2.0 True False
False
In Java, Strings objects are mutable True False
False, when concatenating or modifying a String object, another String object is created
Match the types of arrays to their definitions. Fixed stack-dynamic array Stack-dynamic array Fixed heap-dynamic array Static Array Heap-dynamic array A. An array in which both the subscript ranges and the storage allocation are dynamically bound at elaboration time. B. An array in which the subscript ranges and the storage bindings are both fixed after storage is allocated. Additionally, both the subscript ranges and storage bindings are done when the user program requests them during execution, and the storage is allocated from the heap. C. An array in which the subscript ranges are statically bound, but the allocation is done at declaration elaboration time during execution. D. An array in which the subscript ranges are statically bound and storage allocation is static (done before run time). E. An array in which the binding of subscript ranges and storage allocation is dynamic and can change any number of times during the array's timeline.
Fixed stack-dynamic array - C Stack-dynamic array - A Fixed heap-dynamic array - B Static Array - D Heap-dynamic array - E
Using the algorithm described in Section 4.4.2, remove direct left recursion form the following grammar rules. X → Xyy | Xz | Yx | w Y → Yy | Yw | zy | x
For X: A = X, α _1 = yy, α _2 = z, β_1 = Yx, β_2 = w X -> YxX' | wX' X' -> yyX' | zX' | Ɛ For X: A = Y, α _1 = y, α _2 = w, β_1 = zy, β_2 = x Y -> zyY' | xY' Y' -> yY' | wY' | Ɛ
What is an alias?
If two variable names can be used to access the same memory location, they are called aliases
Unlike the C family of languages that use curly braces to delineate blocks of code, Python use _______ to indicate a statement's membership in a block.
Indentation
What is the purpose of the 'let' constructs in functional languages?
It binds names to values in order to be used in an expression
Variables cam be characterized as a sextuple (6-tuple) of which six attributes?
Name Address Value Type Lifetime Scope
What is the potential danger of case-sensitive names?
Names that look alike are different
Are the tuples of Python mutable? Yes No
No
Are the unions of Ada always type checked? Yes No
No
Convert the following EBNF rules to BNF: S → A{bA} A → a[b]A
S -> A | AB A -> aA -> abA B -> bA | BbA
Using the grammar in Example 3.2 [p.117]*, draw a parse tree for each of the three following statements: a. A = A * (B + (C * A)) b. B = C * (A * C + B) c. A = A * (B + (C))
See Notes. Right now, not later.
Using the grammar in Example 3.4 [p.120]*, draw a parse tree for each of the four following statements: a. A = ( A + B ) * C b. A = B + C + A c. A = A * (B + C) d. A = B * (C * (A + B))
See Notes. Right now, not later.
What are three reasons why lexical analysis is separated from syntax analysis? (one word each)
Simplicity Efficiency Portability (Textbook page 169 maybe look at these in more detail)
Define lifetime, scope, and dynamic scope.
The lifetime of a variable is the time during which it is bound to a particular memory cell. The scope of a variable can be statically determined (prior to execution). Dynamic scope is based on the calling sequence of subprograms, not on their spatial relationship to each other. Thus, the scope can be determined only at run time.
A selection statement provides the means of choosing between two or more paths of execution. True False
True
A tuple is a data type that is similar to a record, except that the elements are not named. True False
True
In Racket, an "if" control statement requires an else option. True False
True
It is possible to use a loop counter variable in a recursive loop. True False
True
What is the boolean evaluation of the following C++ expression? 3 < 2 < 1 True False
True
What is the boolean evaluation of this C-style expression in red? int x = 3; int y = 2; if (y++ && y++==x) { ... } True False
True
It is possible to use a loop counter variable in a while loop True False
True Ex: int x = 0; // x is the loop counter variable while(x < 10) print x;
Are the unions of F# discriminated? Yes No
Yes
Using the grammar in Example 3.2 [p.117]*, show a sentential form leftmost derivation for each of the three following statements. a. A = A * (B + (C * A)) b. B = C * (A * C + B) c. A = A * (B + (C))
a. <assign> => <id> = <expr> => A = <expr> => A = <id> * <expr> => A = A * <expr> => A = A * (<expr>) => A = A * (<id> +<expr>) => A = A * (B + <expr>) => A = A * (B + (<expr>)) => A = A * (B + (<id> * <expr>)) => A = A * (B + (C * <expr>)) => A = A * (B + (C * <id>)) => A = A * (B + (C * A)) b. <assign>=> <id> = <expr> => B = <expr> => B = <id> * <expr> => B = C * <expr> => B = C * (<expr>) => B = C * (<id> * <expr>) => B = C * (A * <expr>) => B = C * (A* <id> + <expr>) => B = C * (A* C + <expr>) => B = C * (A* C + <id>) => B = C * (A* C + B) c. <assign> => <id> = <expr> => A = <expr> => A = <id> * <expr> => A = A * <expr> => A = A * (<expr>) => A = A * (<id> + <expr>) => A = A * (B + <expr>) => A = A * (B + (<expr>)) => A = A * (B + (<id>)) => A = A * (B + (C))
Compute the weakest precondition for each of the following assignment statements and postconditions: a. a = 2 * (b - 1) - 1 {a > 0} b. b = (c + 10) / 3 {b > 6} c. a = a + 2 * b - 1 {a > 1} d. x = 2 * y + x - 1 {x > 11}
a. 2(b-1) -1 > 0 2b - 2 - 1 > -0 2b -3 > 0 2b > 3 b > 3/2 b. (c+10) / 3 > 6 c + 10 > 18 c > 8 c. a + 2b - 1 > 1 a + 2b > 2 2b > 2 - a b > 1 - a/2 d. 2y + x - 1 > 11 2y + x > 12 2y > 12 - x y > 6 - x/2
Using the grammar in Example 3.4 [p.120]*, show a sentential form leftmost derivation for each of the four following statements. a. A = ( A + B ) * C b. A = B + C + A c. A = A * (B + C) d. A = B * (C * (A + B))
a. <assign> => <id> = <expr> => A = <expr> => A = <term> => A = <term> * <factor> => A = <factor> * <facor> => A = (<expr>) * <factor> => A = (<expr> + <term>) * <factor> => A = (<term> + <term>) * <facor> => A = (<factor> + <term>) * <factor> => A = (<id> + <term>) * <factor> => A = (A + <term>) * <factor> => A = (A + <factor>) * <factor> => A = (A + <id>) * <factor> => A = (A + B) * <factor> => A = (A + B) * <id> => A = (A + B) * C b. <assign>=> <id> = <expr> => A = <expr> => A = <expr> + <term> => A = <expr> + <term> + <term> => A = <term> + <term> + <term> => A = <factor> + <term> + <term> => A = <id> + <term> + <term> => A = B + <term> + <term> => A = B + <factor> + <term> => A = B + <id> + <term> => A = B + C + <term> => A = B + C + <factor> => A = B + C + <id> => A = B + C + A c. <assign>=> <id> = <expr> => A = <expr> => A = <term> => A = <term> * <factor> => A = <factor> * <facor> => A = <id> * <factor> => A = A * <factor> => A = A * (<expr>) => A = A * (<expr> + <term>) => A = A * (<term> + <term>) => A = A * (<factor> + <term>) => A = A * (<id> + <term>) => A = A * (B + <term>) => A = A * (B + <factor>) => A = A * (B + <id>) => A = A * (B + C) d. <assign>=> <id> = <expr> => A = <expr> => A = <term> => A = <term> * <factor> => A = <factor> * <factor> => A = <id> * <factor> => A = B * <factor> => A = B * (<expr>) => A = B * (<term>) => A = B * (<term> * <factor>) => A = B * (<factor> * <factor>) => A = B * (<id> * <factor>) => A = B * (C * <factor>) => A = B * (C * (<expr>)) => A = B * (C * (<expr> + <term>)) => A = B * (C * (<term> + <term>)) => A = B * (C * (<factor> + <term>)) => A = B * (C * (<id> + <term>)) => A = B * (C * (A + <term>)) => A = B * (C * (A + <factor>)) => A = B * (C * (A + <id>3)) => A = B * (C * (A + B))
Perform the pairwise disjointness test for each of the following grammar rules. Your answer should show the FIRST() function for each RHS, and then state whether the LHS rule passes or fails pairwise disjointness by examining all pairs of RHS FIRST()'s. a. A → aB | b | cBB b. B → aB | bA | aBb c. C → aaA | b | caB
a. FIRST(aB) = {a} FIRST(b) = {b} FIRST(cBB) = {c} FIRST(aB) ∩ FIRST(b) ∩ FIRST(cBB) = Ø {a} ∩ {b} ∩ {c} = Ø The LHS rule A passes pairwise disjointness. b. FIRST(aB) = {a} FIRST(bA) = {b} FIRST(aBb) = {a} FIRST(aB) ∩ FIRST(bA) ∩ FIRST(aBb) = {a} {a} ∩ {b} ∩ {a} = {a} fails since FIRST(aB) = {a} and FIRST(aBb) = {a} do not have unique symbols c. FIRST(aaA) = {a} FIRST(b) = {b} FIRST(caB) = {c} FIRST(aaA) ∩ FIRST(b) ∩ FIRST(caB) = Ø {a} ∩ {b} ∩ {c} = Ø Passes since every FIRST is unique.
Perform the pairwise disjointness test for each of the following grammar rules. Your answer should show the FIRST() function for each RHS, and then state whether the LHS rule passes or fails pairwise disjointness. a. S → aSb | bAA b. A → b{aB} | a c. B → aB | a
a. FIRST(aSb) = {a} FIRST(bAA) = {b} FIRST(aSb) ∩ FIRST(bAA) = Ø {a} ∩ {b} = Ø Passes b. FIRST(b{aB}) = {b} FIRST(a) = {a} FIRST(b{aB}) ∩ FIRST(a) = Ø {b} ∩ {a} = Ø Passes c. FIRST(aB) = {a} FIRST(a) = {a} FIRST(aB) ∩ FIRST(a) = {a} {a} ∩ {a} = {a} Fails since FIRST(aB) = {a} and FIRST(a) = {a} are not unique .
What is the output of the following Perl code: $x = 0; $y = 1; $z = 2; if ($z/$y || $z/$x) { print "hello"; } else { print "bye"; } a. "hello" b. null output (no error, but no output) c. "bye" d. divide by zero error
a. "hello"
What is the output of the following Python code? x = 1 while(x<10): x += x print x a. 16 b. 9 c. 10 d. 8
a. 16
What is the output of the following C++ code ? int i[ ] = {3,6,9}; cout << *i+1; a. 4 b. 3 c. 6 d. 0x7f3e5029254c i.e. some hexadecimal memory address
a. 4
What is the output of the following C++ code? int i[] = {3,6,9}; cout << (*i)+1; a. 4 b. 3 c. 6 d. 0x7f3e5029254c i.e. some hexadecimal memory address
a. 4
Consider the following C program: int fun(int *i) { *i += 5; return 4; } int main() { int x = 3; x = x + fun(&x); std::cout << x << std::endl; } What is the value of x displayed in the std::cout line after the assignment statement in main, assuming a. operands are evaluated left to right. [a] b. operands are evaluated right to left. [b]
a. 7 b. 12
In Perl, an associative array is called a a. Hash b. Grid c. Correlation d. Map
a. Hash
Which language below allows arrays to have negative integer indices? a. Perl b. C++ c. Python d. Java
a. Perl c. C++
According to your textbook, what are the two distinct kinds of uses for pointers? a. Pointers provide some of the power of indirect addressing. b. Pointers provide a way to manage dynamic storage. c. Pointers increase the storage capacity of variables. d. Pointers provide a safe mechanism to modify constants.
a. Pointers provide some of the power of indirect addressing b. Pointers provide a way to manage dynamic storage
Select all that are examples of dynamic type binding. a. Python x = int(4.0) b. C++ int x = 4; c. Perl $x = 4; d. Java int x = (int)4.0;
a. Python c. Perl (Notice we don't have to specify variable type)
At which possible binding time is the Java + operator symbol bound to a memory location? a. Language design time b. Runtime c. Compile time d. Load time e. Language implementation time
a. language design time
At which possible binding time is a C or C++ static variable bound to a memory location? a. Load time b. Compile time c. Runtime d. Language design time e. Language implementation time
a. load time
A union is a data type a. whose variables may store different type values at different times during program execution. b. composed of a combination (or "union") of other types. c. that is a pointer to a memory address. d. that is a pair of values of the same type.
a. whose variables may store different type values at different times during program execution.
Consider the following grammar: S → aScB | A | b A → cA | c B → d | A Which of the following sentences are in the language generated/recognized by this grammar? acccbd accc abcd acccbcc acd cd
accc abcd
What is the value of x after the following C-style snippet? int y = 2; int z = 4 - y; x = (y == z) ? 3 : 1 a. 1 b. 3 c. 4 d. 2
b. 3
Which languages DO NOT support coercion in expressions? a. Java b. F# c. Perl d. ML
b. F# d. ML
Which of the following is not a value used by a loop variable in counter-controlled loops? a. Terminal value b. Recursion value c. Initial value d. Step size value
b. Recursion value
What is the primary use of attribute grammars? a. Defining dynamic semantics b. Enforcing type compatibility c. Enforcing BNF syntax rules d. Limiting memory usage
b. enforcing type compatability
A programming language is strongly typed a. type errors are detected when variables are instantiated. b. type errors are always detected. c. type errors are detected when coercion or casting is attempted. d. type errors are detected when variables are passed as parameters to functions/methods.
b. type errors are always detected.
Consider the following grammar: <S> → <A> a <B> b <A> → <A> b | b <B> → a <B> | a Which of the following strings are in the language generated by this grammar? baab bbbab bbaab bbaaaaa
baab bbaab
What is the value of $x after the execution of the following Perl code? $x = 0; $y = 1; $z = 2; ($x ? $y : $z) = 3; a. 1 b. 2 c. 0 d. 3
c. 0
What is the output of the following C++ code? int i[] = {3,6,9}; cout << *(i+1); a. 4 b. 3 c. 6 d. 0x7f3e5029254c i.e. some hexadecimal memory address
c. 6
On what branch of mathematics is axiomatic semantics based? a. Combinatorics b. Recursive Function Theory c. Formal Logic d. Linear Algebra
c. Formal Logic
On what branch of mathematics is denotational semantics based? a. Formal logic b. Combinatorics c. Recursive Function Theory d. Linear Algebra
c. Recursive function theory
The values of enumeration constants a. are randomly assigned by the compiler. b. are mapped to memory locations, but not any specific data values. c. can be explicitly assigned any integer literal in the type's definition. d. are always mapped to integers beginning at 0, 1, 2, ...
c. can be explicitly assigned ANY integer literal in the type's definition.
A programming language is strongly typed if a. type errors are checked when variables are passed as function arguments b. all type declarations are explicit c. type errors are always checked d. all type declarations are explicit and static
c. type errors are always checked
What is the output of the following C++ code? int i[] = {3,6,9}; cout << *&i; a. 4 b. 3 c. 6 d. 0x7f3e5029254c i.e. some hexadecimal memory address
d. 0x7f3e5029254c i.e. some hexadecimal memory address
What is the output of the following C++ code? int i[] = {3,6,9}; cout << (i+1); a. 4 b. 3 c. 6 d. 0x7f3e5029254c i.e. some hexadecimal memory address
d. 0x7f3e5029254c i.e. some hexadecimal memory address
What is the evaluation of this Racket code? (define z 2) (let ((x 3)(y 5)) (+ (* x y) z)) a. 25 b. 30 c. 15 d. 17
d. 17
An early programming language whose control statements were based on the IBM 704 hardware. a. APL b. Lisp c. COBOL d. Fortran I
d. Fortran
In Java, the else option of an if control statement is bound to _____. a. The innermost if. b. The outermost if. c. The if inside of curly braces. d. The nearest previous if.
d. The nearest previous if.
An associative array is an unordered collection of data elements that are indexed by a. a defined, enumerated list. b. the Dewey Decimal System. c. memory locations. d. an equal number of values called keys, which may be strings or numerics.
d. an equal number of values called keys, which may be strings or numerics.
An explicit type conversion is called a. coercion b. translation c. mapping d. casting
d. casting
The switch keyword that introduces a clause to handle unrepresented values in a C++ switch is
default
Which of the following are signed integers in Java? a. float b. bit c. boolean d. double e. int f. long g. byte h. short
e. int f. long g. byte h. short
