Chapter 6 - programming Language

Review Question : 
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6. What are the advantages of user-defined enumeration types?

• The advantages are readability and reliability.

7.In what ways are the user-defined enumeration types of C# more reliable than those of C++?

• C# enumeration types are like those of C++, except that they are never coerced to integer. So, operations on enumeration types are restricted to those that make sense. Also, the range of values is restricted to that of the particular enumeration type.

8. What are the design issues for arrays?
The primary design issues specific to arrays are the following:

• What types are legal for subscripts?
• Are subscripting expressions in element references range checked?
• When are subscript ranges bound?
• When does array allocation take place?
• Are ragged or rectangular multidimensioned arrays allowed, or both?
• Can arrays be initialized when they have their storage allocated?
• What kinds of slices are allowed, if any?

9 Define static, fixed stack-dynamic, stack-dynamic, fixed heap-dynamic, and heap-dynamic arrays. What are the advantages of each?

• Static: subscript ranges are statically bound and storage allocation is static (before run-time). Advantage: efficiency (no dynamic allocation). 
• Fixed stack-dynamic: subscript ranges are statically bound, but the allocation is done at declaration time. Advantage: space efficiency. 
• Stack-dynamic: subscript ranges are dynamically bound and the storage allocation is dynamic (done at run-time). Advantage: flexibility (the size of an array need not be known until the array is to be used). 
• Fixed heap-dynamic: similar to fixed stack-dynamic: storage binding is dynamic but fixed after allocation. Advantage: space efficiency, storage is allocated from heap, and binding is done when requested. 
• Heap-dynamic: binding of subscript ranges and storage allocation is dynamic and can change any number of times. Advantage: flexibility (arrays can grow or shrink during program execution).

10. What happens when a nonexistent element of an array is referenced

in Perl?

• No error will be reported

Programming Language :

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6. Explain all of the differences between Ada’s subtypes and derived types.

• A subtype is compatible with its base type, so you can mix operands of the base type with operands of the base type. For example:
• subtype Week_Days is Integer range 1..7; Since this is a subtype, you can (for example) add 1 to a weekday to get the next weekday.
• A derived type is a completely separate type that has the same characteristics as its base type. You cannot mix operands of a derived type with operands of the base type. If, for example, you used:
• type Week_Day is new Integer range 1..7;  Then you would not be able to add an integer to a weekday to get another weekday. To do manipulations on a derived type, you'd normally define those manipulations yourself (e.g., create a package). At the same time, a derived type does "inherit" all the operations of its base type (even some that may not make sense) so you do still get addition.

7.What significant justification is there for the -> operator in C and C++?

• The only justification for the -> operator in C and C++ is writability. It is slightly easier to write p -> q than (*p).q.

8.What are all of the differences between the enumeration types of C++ and those of Java?

• In C++, an enumeration is just a set of named, integral constants. In Java, an enumeration is more like a named instance of a class. You have the ability to customize the members available on the enumeration.Also, C++ will implicitly convert enum values to their integral equivalent, whereas the conversion must be explicit in Java.

9.The unions in C and C++ are separate from the records of those languages, rather than combined as they are in Ada. What are the advantages and disadvantages to these two choices?

• Ada :
• Advantage:
• Unconstrained variant records in Ada allow the values of their variants to change types during execution.

• disadvantage:
• However, the type of the variant can be changed only by assigning the entire record, including the discriminant. This disallows inconsistent records because if the newly assigned record is a constant data aggregate, the value of the tag and the type of the variant can be statically checked for consistency.

10. Multidimensional arrays can be stored in row major order, as in C++, or in column major order, as in Fortran. Develop the access functions for both of these arrangements for three-dimensional arrays.

• Let the subscript ranges of the three dimensions be named min(1), min(2), min(3), max(1), max(2), and max(3). Let the sizes of the subscript ranges be size(1), size(2), and size(3). Assume the element size is 1.
• Row Major Order:
• location(a[i,j,k]) = (address of a[min(1),min(2),min(3)])+((i-min(1))*size(3) + (j-min(2)))*size(2) + (k-min(3))
• Column Major Order:
• location(a[i,j,k]) = (address of a[min(1),min(2),min(3)])+((k-min(3))*size(1) + (j-min(2)))*size(2) + (i-min(1))

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Assignment #5 - Programming Language (Chapter 5)

.: Chapter 5 :.

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6. What is the l-value of a variable? What is the r-value?

• The l-value of variable is the address of a variable because the address is required when the name of a variable appears in the left side of an assignment. While r-value of variable is a variable’s value because it is required when the name of the variable appears in the right side of an assignment statement.

7. Define binding and binding time.

• A binding is an association between an attribute and an entity, such as between a variable and its type or value, or between an operation and a symbol. While the time at which a binding takes place is called binding time.

8. After language design and implementation [what are the four times bindings can take place in a program?]

• First the compile time binding, second the load time binding, third the link time binding and lastly the run time binding.

9. Define static binding and dynamic binding.

• A static binding is when the binding occurs before run time begins and remains unchanged throughout program execution. If the binding first occurs during run time or can change in the course of program execution, it is called dynamic binding.

10. What are the advantages and disadvantages of implicit declarations?

• The advantage of implicit declarations is that Simple in naming conventions. In this case, the compiler or interpreter binds a variable to a type based on the syntactic form of the variable’s name. While the disadvantage of implicit declarations is it can be detrimental to reliability because they prevent the compilation process from detecting some typographical and programmer errors.

Problem Sets:

6. Consider the following JavaScript skeletal program:

// The main program

var x;

function sub1() {

var x;

function sub2() {

…

}

}

function sub3() {

…

}

Assume that the execution of this program is in the following unit order:

main calls sub1

sub1 calls sub2

sub2 calls sub3

a. Assuming static scoping, in the following, which declaration of x is the correct one for a reference to x?

i. sub1

sub1: sub1

ii. sub2

sub2: sub1

iii. sub3

sub3: main

b. Repeat part a, but assume dynamic scoping.

i. sub1

sub1: sub1

ii. sub2

sub2: sub1

iii. sub3

sub3: sub1

7. Assume the following JavaScript program was interpreted using static-scoping rules. What value of x is displayed in function sub1? Under dynamic-scoping rules, what value of x is displayed in function sub1?

var x;
function sub1() {
document.write(“x = ” + x + “<br />”);
}
function sub2() {
var x;
x = 10;
sub1();
}
x = 5;
sub2();

static scoping rule = 5

dynamic scoping rule = 10

8. Consider the following JavaScript program:

var x, y, z;

function sub1() {

     var a, y, z;

function sub2() {

     
var a, b, z;

…

}

…

}

function sub3() {

var a, x, w;

     …

}

List all the variables, along with the program units where they are declared, that are visible in the bodies of sub1, sub2, and sub3, assuming static scoping is used.

Variable                       Where Declared

In Sub1:

a                                             Sub1

y                                             Sub1

z                                             Sub1

x                                             Main

In Sub2:

a                                             Sub2

b                                             Sub2

z                                             Sub2

y                                             Sub1

x                                             Main

In Sub3:

a                                             Sub3

x                                             Sub3

w                                            Sub3

y                                             Main

z                                             Main

9. Consider the following Python program:

x = 1;

y = 3;

z = 5;

def sub1():

a = 7;

y = 9; z = 11;

…

def sub2():

global x;

a = 13;

x = 15;

w = 17;

…

def sub3():

nonlocal a;

a = 19;

b = 21;

z = 23;

…

…

List all the variables, along with the program units where they are declared, that are visible in the bodies of sub1, sub2, and sub3, assuming static scoping is used.

Variable                       Where Declared

In Sub1:

a                                              Sub1

y                                              Sub1

z                                              Sub1

x                                              Main

In Sub2:

a                                              Sub2

x                                              Sub2

w                                             Sub2

y                                              Main

z                                              Main

In Sub3:

a                                              Sub3

b                                              Sub3

z                                              Sub3

w                                             Sub2

x                                              Sub2

y                                              Main

10. Consider the following C program

void fun(void) {

int a, b, c; /* definition 1 */

…

while (. . .) {

int b, c, d; /* definition 2 */

. . . <———– 1

while (. . .) {

int c, d, e; /* definition 3 */

. . . <———– 2

}

. . . <———– 3

}

. . . <———— 4

}

For each of the 4 marked points, list all visible variables, along with the number of the definition statement that defines it.

Point 1: a =1, b = 2, c = 2, d = 2

Point 2: a =1, b = 2, c = 3, d = 3, e = 3

Point 3: a = 1, b = 2, c = 2, d = 2

Point 4: a = 1, b = 1, c = 1

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