Programming Chapter 8: Control Structures

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Questions and Answers

A control structure includes both control statements and the statements whose execution it controls.

True

Two-way selection statements can only choose between two paths of execution with no other options.

False

In C89, Boolean expressions were used as control expressions.

False

Contemporary languages like Java and C# require only Boolean expressions for control expressions.

True Signup and view all the answers

Fortran's arithmetic IF is a contemporary feature used to control different paths based on an arithmetic expression's value.

False Signup and view all the answers

In most contemporary languages, the then and else clauses can only be single statements.

False Signup and view all the answers

Nesting selectors in Java allows the else clause to be paired with the nearest unpaired then clause.

True Signup and view all the answers

In Perl, all then and else clauses must be single statements.

False Signup and view all the answers

The inner if-then structure in Java requires a simple statement to force alternative semantics.

False Signup and view all the answers

The switch statement in C++ allows implicit branches at the end of code segments.

False Signup and view all the answers

In C#, every selectable segment in a switch statement must end with an explicit unconditional branch statement.

True Signup and view all the answers

FORTRAN's arithmetic IF statement allows for segment selection based on a Boolean expression.

False Signup and view all the answers

Ada's elsif construct improves the readability compared to nested two-way selectors.

True Signup and view all the answers

A default clause in a switch statement provides a fallback for unrepresented values.

True Signup and view all the answers

Iterative statements can repeat execution zero times.

False Signup and view all the answers

The C switch statement prohibits executing more than one segment unintentionally.

True Signup and view all the answers

Iteration in computer programming is primarily accomplished through recursion rather than iteration.

False Signup and view all the answers

The loop parameters include the initial value, terminal value, and stepsize of the loop variable.

True Signup and view all the answers

A pretest loop means that the loop completion occurs after the loop body is executed.

False Signup and view all the answers

Counter-controlled loops maintain control with a loop variable known as the loop var.

True Signup and view all the answers

The do-while loop in programming languages guarantees that the loop body executes at least once.

True Signup and view all the answers

The for statement in C-based languages cannot include multiple statements in its expressions.

False Signup and view all the answers

C and C++ do not provide an unconditional branch statement.

False Signup and view all the answers

Logical control of loops only allows for pretest condition checking.

False Signup and view all the answers

Java allows unrestricted use of the goto statement.

False Signup and view all the answers

The continue statement in C and C++ transfers control to the end of the loop.

False Signup and view all the answers

The location of the control mechanism in a loop can be at the top or the bottom of the loop.

True Signup and view all the answers

In C# and Java, break statements can be labeled for use in nested loops.

True Signup and view all the answers

Changing the loop variable in the loop body is always illegal and affects loop control.

False Signup and view all the answers

The use of unrestricted goto statements in programming can lead to readable and maintainable code.

False Signup and view all the answers

C# includes the goto statement to control the execution flow in switch statements.

True Signup and view all the answers

User-located loop control mechanisms can allow control to be chosen at locations other than the top or bottom of a loop.

True Signup and view all the answers

What type of selection statement allows choosing between two paths of execution?

Two-way selector Signup and view all the answers

In contemporary programming languages, which type of expressions can be used as control expressions?

Boolean expressions Signup and view all the answers

Which statement regarding the then and else clauses in C-based languages is correct?

They can be enclosed in braces to form compound statements. Signup and view all the answers

In which programming language is the last clause in a selection construct terminated with 'end' and 'if'?

Ada Signup and view all the answers

What is the primary characteristic of the arithmetic IF statement in Fortran?

It directs control based on the sign of an arithmetic expression. Signup and view all the answers

Which statement is true regarding nesting selectors in modern programming languages like Java?

The else clause is paired with the nearest unpaired then clause. Signup and view all the answers

What is one of the design issues concerning control expressions?

The form and type of the control expression. Signup and view all the answers

What distinguishes an unconditional branch statement?

It allows skipping sections of code. Signup and view all the answers

Which of the following correctly describes the requirement for selectable segments in a C# switch statement?

Every selectable segment must end with a break or goto statement. Signup and view all the answers

What is a significant drawback of FORTRAN's arithmetic IF structure?

Selectable segments are dispersed and not easily readable. Signup and view all the answers

What advantage does Ada's elsif construct have over nested two-way selectors?

It improves the readability of deeply nested structures. Signup and view all the answers

What is the function of the default clause in a switch statement?

It provides a fallback execution path for unrepresented values. Signup and view all the answers

Which statement regarding the execution of multiple segments in a selection construct is true?

Many languages allow for multiple segments to be executed in one construct. Signup and view all the answers

What is a common aspect of the switch construct in C, C++, and Java?

The control expression must evaluate to an integer type. Signup and view all the answers

Which of the following best describes an iterative statement?

It enables repeated execution of a statement or compound statement. Signup and view all the answers

How does the structure of Java's inner if-then construct differ when forcing alternative semantics?

It necessitates positioning the inner if-then within a compound statement. Signup and view all the answers

What characterizes a counting iterative control statement?

It includes a variable for maintaining the count value. Signup and view all the answers

In programming, what does the term 'pretest' refer to?

The loop completion occurs before the loop body is executed. Signup and view all the answers

Which of the following is a key design issue for logically controlled loops?

Should the loop be a pretest or posttest? Signup and view all the answers

Which loop structure guarantees at least one execution of the loop body?

Do-While loop Signup and view all the answers

What are the three components referred to as loop parameters in a counter-controlled loop?

Initial value, termination value, stepsize Signup and view all the answers

Which statement is true regarding the C for statement compared to those in Fortran and Ada?

It allows multiple statements in each of its expressions. Signup and view all the answers

What does the stepsize in a counting loop primarily dictate?

The rate at which the loop variable changes. Signup and view all the answers

Which loop mechanism can be either pretest or posttest?

Logical control loops generally Signup and view all the answers

What is a significant difference between the do-while and while loops?

The do-while loop always executes the loop body at least once. Signup and view all the answers

What are unconditional unlabeled exits used for in C and C++?

To exit a loop prematurely without conditions. Signup and view all the answers

Which of the following statements about the goto statement is accurate?

Goto has the potential to make programs more difficult to maintain. Signup and view all the answers

What is one of the design issues regarding user-located loop control mechanisms?

Should the conditional be part of the exit process. Signup and view all the answers

What is the main function of the continue statement in C and C++?

To skip the remainder of the loop body for the current iteration. Signup and view all the answers

What restricts the use of the goto statement in many programming languages?

It often leads to complex and unmanageable code. Signup and view all the answers

Which of the following languages does not support the goto statement?

Java Signup and view all the answers

What is an example of a mechanism for transferring control to the smallest enclosing loop?

The continue statement. Signup and view all the answers

Study Notes

Chapter 8: Statement-Level Control Structures

This chapter covers statement-level control structures in programming.
Control structures direct the execution flow of statements.
Key topics include: introduction, selection statements, iterative statements, and unconditional branching.
Overall design question: What control statements should be used for specific tasks?

Introduction

A control structure contains a control statement and the statements influenced by it.
Types of control structures include: selection statements, iterative statements, and unconditional branching.

Selection Statements

Selection statements choose between two or more paths of execution.
Two general categories:
- Two-way selectors
- Multiple-way selectors
Two-way Selection Statements:
- Basic structure: if control_expression then clause else clause
Design Issues:
- Form and type of the control expression. (Can be arithmetic or boolean expressions depending on the programming language).
- How then and else clauses are specified. (Can be single or compound statements).
- How nested selectors are handled. (The else clause is paired with the nearest unpaired then clause in languages like Java).

The Control Expression

Control expressions are typically in parentheses.
In some older languages (e.g., C89), arithmetic expressions were used as control expressions. Modern languages (e.g., Java, C#) use Boolean expressions.
Fortran uses an arithmetic IF with three possible outcomes based on the sign of the control expression (negative, zero, or positive).

Clause Form

The then and else clauses can appear as either single or block statements.
C-based languages use braces {} to define blocks.
Ada uses end if to terminate selection constructs.
Perl requires all then and else clauses to be compound statements.

Nesting Selectors

The else clause is paired with the nearest unpaired then clause in languages like Java.
Rules for disambiguation exist to prevent ambiguity in nested selection structures.
Specific syntax might be needed to force alternative semantics in Java. For example, using compound statements to nest conditionally.

Multiple Selection Constructs

Multiple selection constructs allow choosing between multiple segments of code.
Key design considerations:
- Form and type of the control expression. (Often integer or enumeration-type expressions).
- How selectable segments are specified. (Typically using case labels or similar keywords).
- Restriction on execution flow. (Often require a break statement to exit a specific case).
- Handling unrepresented expression values. (Use of a default case or similar).

Examples of Multiple Selectors (e.g., `switch` statements)

Languages like C, C++, and Java use a switch statement (or similar constructs).
switch expressions use integer types.
switch statements typically don't have automatic branches at the end of each block.
The segments can be grouped into a sequence, a block, or a compound statement.
The break statement is necessary to exit a case (or segment) to avoid unexpected execution flow.
The default case is used to address values not explicitly handled.
Control is transferred unconditionally from a selected segment. (Often using break or goto statements).

Multiple Selection Using `if`

Early Multiple Selection: FORTRAN arithmetic IF is a three-way selector (using the expression and branching to one of three statements). (N1, N2, N3).
Issues with this approach: lacks encapsulation, and relies on GOTO statements which can decrease code readability and maintainability.
Modern languages provide better ways of encapsulating multiple-option selections, using cleaner structures like if-then-elsif.

The `if-then-elsif` Construct

The if-then-elsif construct is a flexible alternative for managing multiple choices, often more readable than multiple nested if statements. (Example of an if-then-elsif structure given in the provided text).

Iterative Statements

Iterative statements repeatedly execute a statement or block of statements.
Iteration is essential for computational power, and is also used in functional languages via recursion.
General Design Issues:
- How iteration is controlled? (Using counter values, conditional, flags).
- Where the loop control mechanism is located (e.g., top or bottom). (pretest or posttest loops).
Design issues for iteration control statements include:
- loop control method.
- location of the conditional controlling the loop.
- types of construct (pretest, posttest)

Counter-Controlled Loops

Counter-controlled loops maintain a counter variable.
Essential parameters include initialization, terminal values, and increment (step)

The `for` Statement

C-based for loops:
More flexible than counting loops typically used in Fortran and Ada.
Expressions can be more complex and may span multiple statements, including multiple variables and calculations. (e.g. for (i=0; i<10; i++))

Logically Controlled Loops

Loops controlled by conditions:
- while loop (pretest).
- do-while loop (posttest). An important difference is that the do-while loop always executes the loop body at least once.
Difference between the do-while and while is that the do-while loop always executes the body at least once, while the while may not if the condition isn't immediately met.

User-Located Loop Control

Sometimes it's useful to control an iteration differently than from the beginning or end of the loop.
Should the conditional be part of the exit?
Should control be transferable out of more than one loop? (using a labeled break statement, or goto).

Unconditional Branching

Unconditional branching uses goto (or similar constructs) to jump to specific locations in the code.
Unrestricted use of goto statements can create difficult-to-understand and debug code. (Modern languages often restrict the use of goto statements, or avoid them altogether. Alternatives exist for more structured control flow).
Alternatives like break and continue for transferring control in specific contexts. (These alternatives help to improve code maintainability and readability).

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This quiz focuses on chapter 8, which examines statement-level control structures in programming. You'll learn about selection statements, iterative statements, and unconditional branching. Test your knowledge on how to effectively direct the flow of execution in your code.

Programming Chapter 8: Control Structures

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Questions and Answers

A control structure includes both control statements and the statements whose execution it controls.

Two-way selection statements can only choose between two paths of execution with no other options.

In C89, Boolean expressions were used as control expressions.

Contemporary languages like Java and C# require only Boolean expressions for control expressions.

Fortran's arithmetic IF is a contemporary feature used to control different paths based on an arithmetic expression's value.

In most contemporary languages, the then and else clauses can only be single statements.

Nesting selectors in Java allows the else clause to be paired with the nearest unpaired then clause.

In Perl, all then and else clauses must be single statements.

The inner if-then structure in Java requires a simple statement to force alternative semantics.

The switch statement in C++ allows implicit branches at the end of code segments.

In C#, every selectable segment in a switch statement must end with an explicit unconditional branch statement.

FORTRAN's arithmetic IF statement allows for segment selection based on a Boolean expression.

Ada's elsif construct improves the readability compared to nested two-way selectors.

A default clause in a switch statement provides a fallback for unrepresented values.

Iterative statements can repeat execution zero times.

The C switch statement prohibits executing more than one segment unintentionally.

Iteration in computer programming is primarily accomplished through recursion rather than iteration.

The loop parameters include the initial value, terminal value, and stepsize of the loop variable.

A pretest loop means that the loop completion occurs after the loop body is executed.

Counter-controlled loops maintain control with a loop variable known as the loop var.

The do-while loop in programming languages guarantees that the loop body executes at least once.

The for statement in C-based languages cannot include multiple statements in its expressions.

C and C++ do not provide an unconditional branch statement.

Logical control of loops only allows for pretest condition checking.

Java allows unrestricted use of the goto statement.

The continue statement in C and C++ transfers control to the end of the loop.

The location of the control mechanism in a loop can be at the top or the bottom of the loop.

In C# and Java, break statements can be labeled for use in nested loops.

Changing the loop variable in the loop body is always illegal and affects loop control.

The use of unrestricted goto statements in programming can lead to readable and maintainable code.

C# includes the goto statement to control the execution flow in switch statements.

User-located loop control mechanisms can allow control to be chosen at locations other than the top or bottom of a loop.

What type of selection statement allows choosing between two paths of execution?

In contemporary programming languages, which type of expressions can be used as control expressions?

Which statement regarding the then and else clauses in C-based languages is correct?

In which programming language is the last clause in a selection construct terminated with 'end' and 'if'?

What is the primary characteristic of the arithmetic IF statement in Fortran?

Which statement is true regarding nesting selectors in modern programming languages like Java?

What is one of the design issues concerning control expressions?

What distinguishes an unconditional branch statement?

Which of the following correctly describes the requirement for selectable segments in a C# switch statement?

What is a significant drawback of FORTRAN's arithmetic IF structure?

What advantage does Ada's elsif construct have over nested two-way selectors?

What is the function of the default clause in a switch statement?

Which statement regarding the execution of multiple segments in a selection construct is true?

What is a common aspect of the switch construct in C, C++, and Java?

Which of the following best describes an iterative statement?

How does the structure of Java's inner if-then construct differ when forcing alternative semantics?

What characterizes a counting iterative control statement?

In programming, what does the term 'pretest' refer to?

Which of the following is a key design issue for logically controlled loops?

Which loop structure guarantees at least one execution of the loop body?

What are the three components referred to as loop parameters in a counter-controlled loop?

Which statement is true regarding the C for statement compared to those in Fortran and Ada?

What does the stepsize in a counting loop primarily dictate?

Which loop mechanism can be either pretest or posttest?

What is a significant difference between the do-while and while loops?

What are unconditional unlabeled exits used for in C and C++?

Which of the following statements about the goto statement is accurate?

What is one of the design issues regarding user-located loop control mechanisms?

What is the main function of the continue statement in C and C++?

What restricts the use of the goto statement in many programming languages?

Which of the following languages does not support the goto statement?

What is an example of a mechanism for transferring control to the smallest enclosing loop?

Study Notes

Chapter 8: Statement-Level Control Structures

Introduction

Selection Statements

The Control Expression

Clause Form

Nesting Selectors

Multiple Selection Constructs

Examples of Multiple Selectors (e.g., switch statements)

Multiple Selection Using if

The if-then-elsif Construct

Iterative Statements

Examples of Multiple Selectors (e.g., `switch` statements)

Multiple Selection Using `if`

The `if-then-elsif` Construct

The `for` Statement