Chapter 11 - Abstract Data Types and Encapsulation Constructs

Review question 2. Define abstract data type. Answer : data type that satisfies the following conditions: -The representation of objects of the type is hidden from the program units that use the type, so the only direct operations possible on those objects are those provided in the type’s definition. -The declarations of the type and the protocols of the operations on objects of the type, which provide the type’s interface, are contained in a single syntactic unit. The type’s interface does not depend on the representation of the objects or the implementation of the operations. Also, other program units are allowed to create variables of the defined type. 8. What is the difference between private and limited private types in Ada? Answer : Limited private is more restricted form and objects of a type that is declared limited private have no built-in operations. 10. What is the use of the Ada with clause? Answer : With clause makes the names defined in external packages visible; in this case Ada. Text_IO, which provides functions for input of text. 11. What is the use of the Ada use clause? Answer : The with clause makes the names defined in external packages Visible. 12. What is the fundamental difference between a C++ class and an Ada package? Answer : Ada packages are more generalize encapsulations that can define any number of types. 15. What is the purpose of a C++ destructor? Answer : The purpose of a C++ desctructor is as a debugging aid, in which case they simply display or print the values of some or all of the object’s data members before those members are deallocated. 16. What are the legal return types of a desctructor? Answer : Destructor has no return types and doesn’t use return statements. 20. What is the use of limited private types? Answer : An alternative to private types is a more restricted form: limited private types. Nonpointer limited private types are described in the private section of a package specification, as are nonpointer private types. The only syntactic difference is that limited private types are declared to be limited private in the visible part of the package specification. The semantic difference is that objects of a type that is declared limited private have no built-in operations. Such a type is useful when the usual predefined operations of assignment and comparison are not meaningful or useful. For example, assignment and comparison are rarely used for stacks. 21. What are initializers in Objective-C? Answer : The initializers in Objective-C are constructors. 22. What is the use of @private and @public directives? Answer : The use is to specify the access levels of the instance variables in a class definition. 27. Where are all Java methods defined? Answer : All Java methods are defined in a class. 30. What is a friend function? What is a friend class? Answer : a “friend” of a given class is allowed access to public, private, or protected data in that class. Normally, function that is defined outside of a class cannot access such information. Class that can access the private and protected members of the class in which it is declared as a friend. On declaration of friend class all member function of the friend class become friends of the class in which the friend class was declared. Problem set 4. What are the advantages of the nonpointer concept in Java? Any task that would require arrays, structures, and pointers in C can be more easily and reliably performed by declaring objects and arrays of objects. Instead of complex pointer manipulation on array pointers, you access arrays by their arithmetic indices. The Java run-time system checks all array indexing to ensure indices are within the bounds of the array. You no longer have dangling pointers and trashing of memory because of incorrect pointers, because there are no pointers in Java. 10. Which two conditions make data type “abstract”? The representation of objects of the type is hidden from the program units that use the type, so the only direct operations possible on those objects are those provided in the type’s definition. The declarations of the type and the protocols of the operations on objects of the type, which provide the type’s interface, are contained in a single syntactic unit. The type’s interface does not depend on the representation of the objects or the implementation of the operations. Also, other program units are allowed to create variables of the defined type. 12. How are classes in Ruby made dynamic? Classes in Ruby are dynamic in the sense that members can be added at any time. This is done by simply including additional class definitions that specify the new members. Moreover, even predefined classes of the language, such as String, can be extended. 13. Compare and contrast the data abstraction of Java and C++. Java support for abstract data types is similar to that of C++. There are, however, a few important differences. All objects are allocated from the heap and accessed through reference variables. Methods in Java must be defined completely in a class. A method body must appear with its corresponding method header. Therefore, a Java abstract data type is both declared and defined in a single syntactic unit. A Java compiler can inline any method that is not overridden. Definitions are hidden from clients by declaring them to be private. Rather than having private and public clauses in its class definitions, in Java access modifiers can be attached to method and variable definitions. If an instance variable or method does not have an access modifier, it has package access. 19. Compare Java’s packages with Ruby’s modules. In Ruby, the require statement is used to import a package or a module. For example, the extensions package/module is imported as follows. require ‘extensions’ External files may be included in a Ruby application by using load or require. For example, to include the external file catalog.rb, add the following require statement. require “catalog.rb” The difference between load and require is that load includes the specified Ruby file every time the method is executed and require includes the Ruby file only once. In Java, the import statement is used to load a package. For example, a Java package java.sql is loaded as follows. import java.sql.*;

Chapter 10 - Implementing Subprograms

REVIEW QUESTIONS 1. What is the definition used in this chapter for “simple subprograms”? Subprogram cannot be nested and all local variables are static. 4.What is the task of a linker? The task of a linker is to find the files that contain the translated subprograms referenced in that and load them into memory. 8. What kind of machines often use registers to pass parameters? RISC. 11. What is an EP, and what is its purpose? EP is a point or first address of the activation record instance of the main program. It is required to control the execution of a subprogram. 14. What are two potentialproblems with the static-chain method? - It is difficult for a programmer working on a time-critical program to estimate the costs of nonlocal references, because the cost of each reference depends on the depth of nesting between the reference and the scope of declaration. - Subsequent code modifications may change nesting depths, thereby changing the timing of some references, both in the changed code and possibly in code far from the changes. 17. Describe the shallow-access method of implementing dynamic scoping. Shallow access is an alternative implementation method, not an alternative semantics. The semantics of deep access and shallow access are identical. In the shallow-access method, variables declared in subprograms are not stored in the activation records of those subprograms. PROBLEM SET 6. Although local variables in Java methods are dynamically allocated at the beginning of each activation, under what circumstances could the value of a local variable in a particular activation retain the value of previous activation? If the variable is declared as static. Static modifier is a modifier that makes a variable history – sensitive. 8. Pascal allows gotos with nonlocal targets. How could such statements be handled if static chains were used for nonlocal variable access? Finding the correct activation record instance of a nonlocal variable using static links is relatively straightforward. When a reference is made to nonlocal variable, the activation record instance containing the variable can be found by searching the static chain until a static ancestor activation record instance is found that contains the variable. 9. The static-chain method could be expanded slightly by using two static links in each activation record instance where the second points to the static grandparent activation record instance. How would this approach affect the time required for subprogram linkage and nonlocal references? Including two static links would reduce the access time to nonlocals that are defined in scopes two steps away to be equal to that for nonlocals that are one step away. Overall, because most nonlocal references are relatively close, this could significantly increase the execution efficiency of many programs. 11. If a compiler uses the static chain approach to implementing blocks, which of the entries in the activation records for subprograms are needed in the activation records for blocks? There are two options for implementing blocks as parameterless subprograms: One way is to use the same activation record as a subprogram that has no parameters. This is the most simple way, because accesses to block variables will be exactly like accesses to local variables. Of course, the space for the static and dynamic links and the return address will be wasted. The alternative is to leave out the static and dynamic links and the return address, which saves space but makes accesses to block variables different from subprogram locals.

Chapter 9 - Subprograms

Review Questions 1. What are the three general characteristic of subprograms? 2. What does it mean for a subprogram to be active? 5. What languages allow a variable number of parameters ? 7. What is a parameter profile? What is a subprogram protocol? 8. What are formal parameters? What are actual parameters? 9. What are the advantages and disadvantages of the keyword parameter? 10 . What are the differences between a function and a procedure ? 22. What are the design issues for functions? 23. In what ways are coroutines different from conventional subprogram? 24. What is an overloaded subprogram? 26. What is multicast delegate? 32. What exactly is a delegate? 34. What is a closure? Answers: 1. Each subprogram has a single entry point, the calling program unit is suspended during the execution of the called subprogram, which implies that there is only one subprogram in execution at any given time, and control always returns to the caller when the subprogram execution terminates. 2. A subprogram is said to be active if, after having been called, it has begun execution but has not yet completed that execution. 5. C,C++,Perl JavaScript, and Lua. 7. Parameter profile is the number, order, and types of its formal parameters. Subprogram protocol is its parameter profile plus, if it is a function, its return type. In languages in which subprograms have types, those types are defined by the subprogram’s protocol. 8. The parameters in the subprogram header are called formal parameters. Subprogram call statements must include the name of the subprogram and a list of parameters to be bound to the formal parameters of the subprogram. These parameters are called actual parameters. 9. The advantage of keyword parameters is that they can appear in any order in the actual parameter list. The disadvantage to keyword parameters is that the user of the subprogram must know the names of formal parameters. 10. Functions return values while procedure does not, and procedure defines new statements, while function define new user-defined operators. 22. Are side effects allowed and what types of values can be returned. 23. Conventional subprograms are subordinate to their callers. When a routine calls a subprogram, execution suspends at that point in the program and resumes after the subprogram has run to completion. As a result, conventional subprogram invocation is atomic, much like a built-in statement in the programming language. 24. Overloaded subprogram is a subprogram that has the same name as another subprogram in the same referencing environment. 26. Multicast delegate is all of the methods stored in a delegate instance are called in the order in which they were placed in the instance. 32. A delegate is the power and flexibility of method pointers in C# increased by making them objects. 34. Closure is a nested subprogram ant its referencing environment, which together allow the subprogram to be called from anywhere in a program. Problem Set 3. Argue in support of the template functions of C++. How is it different from the template functions in other languages? 6 . Compare and contrast PHP’s parameter passing with that of C#. 8 . Argue against the Java design of not providing operator overloading 12 . Research Jensen’s Device, which was a widely known use of pass-by-name parameters, and write a short description of what it is and how it can be used. 15. How is the problem of passing multidimensional arrays handles by Ada? Answers: 3. C++ templated classes are instantiated to become typed classes at compile time. For example, an instance of the templated Stack class, as well as an instance of the typed class, can be created with the following declaration: Stack myIntStack; However, if an instance of the templated Stack class has already been created for the int type, the typed class need not be created. 6. PHP’s parameter passing is similar to that of C#, except that either the actual parameter or the formal parameter can specify pass-by-reference. Passby- reference is specified by preceding one or both of the parameters with an ampersand. 8. Arithmetic operators are often used for more than one purpose. For example, + usually is used to specify integer addition and floating-point addition. Some languages—Java, for example—also use it for string catenation. This multiple use of an operator is called operator overloading and is generally thought to be acceptable, as long as neither readability nor reliability suffers. 12. Implementing a pass-by-name parameter requires a subprogram to be passed to the called subprogram to evaluate the address or value of the formal parameter. The referencing environment of the passed subprogram must also be passed. This subprogram/referencing environment is a closure. Pass-by-name parameters are both complex to implement and inefficient. They also add significant complexity to the program, thereby lowering its readability and reliability. Because pass-by-name is not part of any widely used language, it is not discussed further here. However, it is used at compile time by the macros in assembly languages and for the generic parameters of the generic subprograms in C++, Java 5.0, and C# 2005. 15. Ada compilers are able to determine the defined size of the dimensions of all arrays that are used as parameters at the time subprograms are compiled. In Ada, unconstrained array types can be formal parameters. An unconstrained array type is one in which the index ranges are not given in the array type definition. Definitions of variables of unconstrained array types must include index ranges. The code in a subprogram that is passed an unconstrained array can obtain the index range information of the actual parameter associated with such parameters.

Chapter 8 - Statement-Level Control Structures

Review Questions 2. What did Bohm and Jocopini prove about flowcharts? It was proven that all algorithms that can be expressed by flowcharts can be coded in a programming languages with only two control statements: one for choosing between two control flow paths and one for logically controlled iterations. 3. What is the definition of block? In Ruby, block is a sequence of code, delimited by either breves or the do and and reserved words. 4. What is/are the design issue(s) for all selection and iteration control statements? There is only one design issue that is relevant to all of the selection and iteration control statements: Should the control structure have multiple entries? 7. Under what circumstances must an F# selector have an else clause? An F# selector have an “else” clause if the “if” expression does return a value. 9. What are the design issues for multiple-selection statements? What is the form and type of the expression that controls the selection? How are the selectable segments specified? How are the case values specified? How should unrepresented selector expression values be handled, if at all? Is execution flow through the structure restricted to include just a single selectable segment? 14. What are the design issues for all iterative control statements? How is the iteration controlled? Where should the control mechanism appear in the loop statement? 15. What are the design issues for counter-controlled loop statements? What are the type and scope of the loop variable? Should it be legal for the loop variable or loop parameters to be changed in the loop, and if so, does the change affect loop control? Should the loop parameters be evaluated only once, or once for every iteration? 21. What are the design issues for logically controlled loop statements? Should the control be pretest or post-test? Should the logically controlled loop be a special form of a counting loop or a separate statement? 23. What are the design issues for user-located loop control mechanisms? Should the conditional mechanism be an integral part of the exit? Should only one loop body be exited, or can enclosing loops also be exited? Problem Set 1. What design issues should be considered for two-way selection statements? The design issues for two-way selectors can be summarized as follows: • What is the form and type of the expression that controls the selection? • How are the then and else clauses specified? • How should the meaning of nested selectors be specified? 4. What are the limitations of implementing a multiple selector from two-way selectors and gotos? A multiple selector can be built from two-way selectors and gotos, but the resulting structures are cumbersome, unreliable, and difficult to write and read. 5. What are the arguments pro and con, for Java’s approach to specify compound statements in control statements? • Compound statements are required in control statements when the body of the if or else clause requires multiple statements. • Java uses braces to form compound statements, which serve as the bodies of if and else clauses. 9. Boolean expressions are necessary in the control statements in Java, as opposed to also allowing arithmetic expressions, as in C++. Give a conditional statement that is correct in C++ but not in Java. int i=10; if( i ) { // block of statements } This block of statement is valid in C++ but not in Java. 11. Explain the advantages and disadvantages of the Java switch statement, compared to C++’s switch statement. The Java variable in the argument of a switch statement can be of type integral ( byte, short etc.), char and String( JDK 1.7 onwards), whereas in C++ the argument can be int or char.

Chapter 7 - Expressions and Assignment Statements

Review Question

1.The operator precedence rules for expression evaluation partially define the order in which the operators of different precedence levels are evaluated. The operator precedence rules for expressions are based on the hierarchy of operator priorities, as seen by the language designer. When an expression contains two adjacent 2 occurrences of operators with the same level of precedence, the question of which operator is evaluated first is answered by the associativity rules of the language. An operator can have either left or right associativity, meaning that when there are two adjacent operators with the same precedence, the left operator is evaluated first or the right operator is evaluated first, respectively.

2.It is a conditional operator that provides a shorter syntax for the if..then..else statement. The first operand is a boolean expression; if the expression is true then the value of the second operand is returned otherwise the value of the third operand is returned.

3.The operators ++ for increment, and –– for decrement, can be used either in expressions or to form stand-alone single-operator assignment statements. They can appear either as prefix operators, meaning that they precede the operands, or as postfix operators, meaning that they follow the operands.

5.Operator with illegal expression.

8.A side effect of a function, naturally called a functional side effect, occurs when the function changes either one of its parameters or a global variable. (A global variable is declared outside the function but is accessible in the function.)

9. coercion is an automatic conversion. For example, if an int variable and a float variable are added in Java, the value of the int variable is coerced to float and a floating-point add is done.

11. In object-oriented programming, operator overloading—less commonly known as operator ad-hoc polymorphism—is a specific case of polymorphism, where different operators have different implementations depending on their arguments. Operator overloading is generally defined by the language, the programmer, or both.

12. A narrowing conversion converts a value to a type that cannot store even approximations of all of the values of the original type. A widening conversion converts a value to a type that can include at least approximations of all of the values of the original type.

28.Cast is explicit type conversions. To specify a cast, the desired type is placed in parentheses just before the expression to be converted.

Problem Set

1. Suppose Type1 is a subrange of Integer. It may be useful for the difference between Type1 and Integer to be ignored by the compiler in an expression.

2.If operands in an expression contains both INTEGER and REAL constants or variables, this is a mixed mode arithmetic expression. In mixed mode arithmetic expressions, INTEGER operands are always converted to REAL before carrying out any computations. As a result, the result of a mixed mode expression is of REAL type. can coercion be used in some cases of type mismatch? Fortran, C, C++, and Perl use coercion rules for mixed-mode assignment that are similar to those they use for mixed-mode expressions; that is, many of the possible type mixes are legal, with coercion freely applied.7 Ada does not allow mixed-mode assignment. In a clear departure from C++, Java and C# allow mixed-mode assignment only if the required coercion is widening.8 So, an int value can be assigned to a float variable, but not vice versa. Disallowing half of the possible mixedmode assignments is a simple but effective way to increase the reliability of Java and C#, relative to C and C++.

3. The elimination of overloaded operators in my favorite language would not be beneficial. Operator overloading is claimed to be useful because it allows the developer to program using notation "closer to the target domain"[1] and allows user-defined types a similar level of syntactic support as types built into the language. It can easily be emulated using function calls; for an example, consider the integers a, b, c:

7. An expression such as a + fun(b)

8. Consider the integer expression A + B + C. Suppose the values of A, B, and C are 20,000, 25,000, and -20,000, respectively. Further suppose that the machine has a maximum integer value of 32,767. If the first addition is computed first, it will result in overflow. If the second addition is done first, thewhole expression can be correctly computed.

10. (a) ( a * ( b – ( 1 + c )1 )2 )3

(b) ( a * ( ( b – 1 )2 / ( c mod d )1 )3 )4

(c) ( ( a – b )5 / ( c & ( d * ( e / ( a – 3 )1 )2 )3 )4 )6

(d) ( – ( a or ( c = ( d and e )1 )2 )3 )4

(e) ( a > ( xor ( c or ( d <= 17 )1 )2 )3 )4 (f) ( – ( a + b )1 )2

Chapter 6 - Data Types

Review Questions

1.A descriptor is the collection of the attributes of a variable.

2.Decimal types have the advantage of being able to precisely store decimal values, at least those within a restricted range, which cannot be done with floating-point. The disadvantages of decimal types are that the range of values is restricted because no exponents are allowed, and their representation in memory is mildly wasteful.

3.- The two most important design issues that are specific to character string types are the following:

• Should strings be simply a special kind of character array or a primitive type?

• Should strings have static or dynamic length?

5.A subrange type is a contiguous subsequence of an ordinal type. An ordinal type is one in which the range of possible values can be easily associated with the set of positive integers. An enumeration type is one in which all of the possible values, which are named constants, are provided, or enumerated, in the definition. The third option is to allow strings to have varying length with no maximum, as in JavaScript, Perl, and the standard C++ library. These are called dynamic length strings. This option requires the overhead of dynamic storage allocation and deallocation but provides maximum flexibility.

6.Enumeration types can provide advantages in both readability and reliability. Readability is enhanced very directly: Named values are easily recognized, whereas coded values are not.

7.C# includes both the references of Java and the pointers of C++. However, the use of pointers is strongly discouraged. In fact, any subprogram that uses pointers must include the unsafe modifier. Note that although objects pointed to by references are implicitly deallocated, that is not true for objects pointed to by pointers. Pointers were included in C# primarily to allow C# programs to interoperate with C and C++ code.

15.An aggregate constant is a nonscalar constant which value never change or are not changed during execution of the program.

18.Arrays are part of most programming languages. The relationship between a reference to an array element and the address of that element is given in an access function, which is an implementation of a mapping.

20.An associative array is an unordered collection of data elements that are indexed by an equal number of values called keys. In the case of non-associative arrays, the indices never need to be stored (because of their regularity). In an associative array, however, the user-defined keys must be stored in the structure. So each element of an associative array is in fact a pair of entities, a key and a value. We use Perl’s design of associative arrays to illustrate this data structure.an associative array?

21.evel numbers in COBOL indicate by their relative values the hierarchical structure of the record. Any line that is followed by a line with a higher-level number is itself a record.

43.A compatible type is one that either is legal for the operator or is allowed under language rules to be implicitly converted by compiler-generated code (or the interpreter) to a legal type.

44. A type error is the application of an operator to an operand of an inappropriate type. For example, in the original version of C, if an int value was passed to a function that expected a float value, a type error would occur (because compilers for that language did not check the types of parameters).

45.A programming language is strongly typed if type errors are always detected. This requires that the types of all operands can be determined, either at compile time or at run time. The importance of strong typing lies in its ability to detect all misuses of variables that result in type errors. A strongly typed language also allows the detection, at run time, of uses of the incorrect type values in variables that can store values of more than one type.

50.Name type equivalence means that two variables have equivalent types if they are defined either in the same declaration or in declarations that use the same type name.

Problem Set

2.The CPU doesn't care whether a byte holds -1 or 15 when it moves it from one place to another. There's no such thing as a "signed move" (to a location of the same size - there is a signed move for larger or smaller destinations). The CPU only cares about the representation when it does arithmetic on the byte. The CPU knows whether to do signed or unsigned arithmetic according to the op-code that you (or the compiler on your behalf) chose.

3.The collection of values that can be represented by a floating-point type is defined in terms of precision and range. Precision is the accuracy of the fractional part of a value, measured as the number of bits. Range is a combination of the range of fractions and, more important, the range of exponents.

5.When implicit dereferencing of pointers occurs only in certain contexts, it makes the language slightly less orthogonal. The context of the reference to the pointer determines its meaning. This detracts from the readability of the language and makes it slightly more difficult to learn.

6.The Boolean or logical data type is a data type, having two values (usually denoted true and false), intended to represent the truth values of logic and Boolean algebra. It is named after George Boole, who first defined an algebraic system of logic in the mid-19th century. The Boolean data type is the primary result of conditional statements, which allow different actions and change control flow depending on whether a programmer-specified boolean condition evaluates to true or false. C++ has a separate Boolean data type ('bool'), but with automatic conversions from scalar and pointer values that are very similar to those of C. This approach was adopted also by many later languages, especially by some scripting ones such as AWK. One problem with this approach is that the tests if(t==TRUE){...} and if(t) are not equivalent. Python has a related situation, where the Boolean type, bool is a subtype of the integer type, int, and Booleans False and True act as 0 and 1, respectively, in arithmetic contexts.

8.In their quest for increased safety over C++, the designers of Java removed C++-style pointers altogether. Unlike C++ reference variables, Java reference variables can be assigned to refer to different class instances; they are not constants. All Java class instances are referenced by reference variables. That is, in fact, the only use of reference variables in Java.

16.C and C++ are not strongly typed languages because both include union types, which are not type checked. ML is strongly typed, even though the types of some function parameters may not be known at compile time. F# is strongly typed. Java and C#, although they are based on C++, are strongly typed in the same sense as Ada. Types can be explicitly cast, which could result in a type error. However, there are no implicit ways type errors can go undetected.

Chapter 5 - Names, Bindings, and Scopes

Review Question

1. - The following are the primary design issues for names:

• Are names case sensitive?

• Are the special words of the language reserved words or keywords?

These issues are discussed in the following two subsections, which also include examples of several design choices.

2. - In that sense, case sensitivity violates the design principle that language constructs that look similar should have similar meanings. But in languages whose variable names are case-sensitive, although Rose and rose look similar, there is no connection between them.

3.- A reserved word is a special word of a programming language that cannot be used as a name. As a language design choice, reserved words are better than keywords because the ability to redefine keywords can be confusing.

6.-value is the address of a variable. r-value is a variable’s value that’s required when the name of the variable appears in the right side of an assignment statement.

7. A binding is an association between an attribute and an entity, such as etween a variable and its type or value, or between an operation and a symbol. The time at which a binding takes place is called binding time. Binding and binding times are prominent concepts in the semantics of programming languages.

16. The referencing environment of a statement is the collection of all variables that are visible in the statement.

Problem Set

1.The valid identifier names are _Student, Student, and Student123. We cannot use ‘int’ as name because it’s a reserved keyword and we cannot use the 123Student because C doesn’t allow identifier format with a digit at the first letter.

2.n lvalue is a way of describing the term on the left hand side of an assignment. It is usually an address or variable.

if (0 = foo)

{

}

4.A data type, such as int in C, is bound to a range of values at language implementation time. At compile time, a variable in a Java program is bound to a particular data type. A variable may be bound to a storage cell when the program is loaded into memory. That same binding does not happen until run time in some cases, as with variables declared in Java methods. A call to a library subprogram is bound to the subprogram code at link time.