Java Loops Overview

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Questions and Answers

What is the purpose of using loops in programming?

To define variables.

To create data structures.

To repeat execution of code until a condition is met. (correct)

To execute a block of code only once.

Which of the following describes a counter-controlled repetition?

It executes a fixed number of times known before the loop begins. (correct)

It can run indefinitely without a defined exit.

It terminates after encountering a sentinel value.

It requires user input to determine when to end.

How does a while loop behave when its condition is initially false?

It creates an infinite loop.

It executes the loop body multiple times.

It executes the loop body at least once.

It does not execute the loop body at all. (correct)

What is a sentinel-controlled repetition?

A loop that continues until a specific sentinel value is encountered. Signup and view all the answers

In a do-while loop, which statement is true?

The loop always executes at least once regardless of the condition. Signup and view all the answers

What distinguishes a while loop as a pre-test loop?

It checks the condition before executing the loop body. Signup and view all the answers

Which of the following correctly describes the syntax of a while loop?

while (condition) { statements; } Signup and view all the answers

What will happen if a break statement is encountered inside a loop?

The loop will immediately terminate. Signup and view all the answers

What is the purpose of a sentinel value in a while loop?

To indicate the end of data entry. Signup and view all the answers

What determines the number of times a sentinel-controlled while loop executes?

An input value that signifies when to stop. Signup and view all the answers

What is typically the first step in designing a loop?

Identify the statements that need to be repeated. Signup and view all the answers

In the context of counter-controlled loops, what is the final value of 'count' after the following code executes? 'int count = 1; while (count < 10) { count++; }'

10 Signup and view all the answers

What type of repetition would you use if the number of executions is not known before entering the loop?

Indefinite repetition. Signup and view all the answers

What common programming error is shown in the following code snippet? 'int count = 0; while (count <= 10) { count++; }'

Loop executes one additional time than expected. Signup and view all the answers

How should a sentinel value be chosen to avoid confusion during input?

Use a value that is not allowed as a valid input. Signup and view all the answers

What should be included in the loop-continuation-condition for a typical while loop?

A condition that returns true while the loop should run. Signup and view all the answers

What is the purpose of the sentinel value in the class-averaging program?

To signify the end of input Signup and view all the answers

How does a do...while loop differ from a while loop?

It executes at least once before checking the condition Signup and view all the answers

Which statement is true about the for loop?

It is a counter-controlled repetition loop Signup and view all the answers

What is executed after each iteration of a for loop?

The update expression Signup and view all the answers

What defines a pre-test loop?

The condition is evaluated before the loop body executes Signup and view all the answers

What will happen if the condition of a while loop is false from the beginning?

The loop body will not execute at all Signup and view all the answers

In the context of loops, what does the term 'iteration' refer to?

The execution of the loop body once Signup and view all the answers

What is the role of the loop counter in a for loop?

To control the number of iterations Signup and view all the answers

Study Notes

Why Loops?

Loops are useful to repeat code multiple times.
Example: To print the phrase "Welcome to Java!" 100 times.
Loops are also used to iterate over data structures and collections.

Types of Loops

Counter-controlled repetition (definite repetition):
- Repeats a block of code a fixed number of times.
- Often used when the number of iterations is known beforehand.
Sentinel-controlled repetition (indefinite repetition):
- Repeats a block of code until a specific "sentinel" value is encountered.
- Used when the number of iterations is unknown beforehand.

Loop Statements in Java:

Java offers three loop statements:
- for loop: Executes a known number of times.
- while loop: Continuously executes a block of code while a condition is true.
- do-while loop: Executes a block of code at least once, before checking the condition.

`while` Loop:

Syntax: while(condition) { // code to be repeated }
Evaluates a condition before each iteration.
Executes the code block within the braces if the condition is true.
Terminates when the condition evaluates to false.

`while` Loop - Counter-Controlled Repetition Example:

while loops can be used for counter-controlled iteration, often used along with a control variable.
Example: printing numbers from 1 to 10 using a counter variable.

`while` Loop - Sentinel-Controlled Repetition Example:

Used when the number of iterations is unknown beforehand.
A "sentinel" value is used to signal the end of the loop.
Example: calculating the average of exam scores entered by the user, using -1 as the sentinel value to indicate the end of input.

`do-while` Loop:

Syntax: do { // code to be repeated } while (condition);
Executes the code block once, before evaluating the condition.
If the condition is true, the loop continues iterating.

`for` Loop:

Syntax: for (initialization; condition; update) { // code to be repeated }
Ideal for counter-controlled repetition.
Initialization: Executed once at the beginning of the loop.
Condition: Checked before each iteration; loop continues if it is true.
Update: Executed after each iteration.
Example: printing numbers from 1 to 10 using a for loop.

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Description

This quiz covers the fundamentals of loops in Java, including counter-controlled and sentinel-controlled repetitions. It explains the different types of loop statements—'for', 'while', and 'do-while'—and their uses in programming. Test your understanding of how loops work and their syntax in Java.