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Chapter 4: Problem 29

( Square of Asterisks) Write an application that prompts the user to enter the size of the side of a square, then displays a hollow square of that size made of asterisks. Your program should work for squares of all side lengths between 1 and 20 .

Short Answer

Expert verified
Prompt the user for an integer (1-20), and use loops to print a line of asterisks for the top, sides filled with spaces and bounded by asterisks, and a line of asterisks for the bottom.

Step by step solution

01

Prompt for Side Length

Request the user enters an integer for the size of the square's side, ensuring it's between 1 and 20. Validate the input to make sure it's within the acceptable range.
02

Print the Top of the Square

Use a loop to print the top side of the square by outputting the number of asterisks equal to the side length.
03

Print the Sides of the Square

Use nested loops to print the sides of the square. The outer loop controls the lines, and the inner loops print spaces between asterisks. For lines between the top and bottom, print an asterisk, followed by spaces, and then another asterisk.
04

Print the Bottom of the Square

Use a loop to print the bottom side of the square with asterisks if the side length is more than 1. This step is similar to Step 2.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Conditional Statements in Java
Conditional statements are the backbone of decision-making in Java. They allow a program to take different actions based on whether a specified condition is true or false. One of the most common conditional statements in Java is the 'if' statement, which is used to evaluate a condition. For example, when verifying the size of a square's side, an 'if' statement can check if the input is within the range of 1 to 20.

In the context of the application described, conditional statements are crucial. When a user inputs a number, the 'if' statement checks:
  • If the number is less than 1 or greater than 20, the program can prompt the user to re-enter a valid number.
  • If the number is within range, it proceeds to the next steps of printing the square.
The use of conditional statements ensures that the program behaves correctly and predictably, handling improper input gracefully.
Input Validation
Input validation is an essential aspect of programming that involves checking if the input provided by a user meets certain criteria before processing it. In our Java application to print a square, input validation is used to ensure that the size of the square's side is between 1 and 20. This not only prevents errors during the execution of subsequent steps but also guards against unintended or malicious input.

To improve user experience and program robustness, input validation generally includes:
  • Checking the data type of the input to ensure it's an integer.
  • Ensuring the value falls within the accepted range.
  • Providing clear feedback to the user if the entered value is invalid.
  • Allowing users to re-enter a valid value without having to restart the program.
Effective input validation is critical for maintaining the integrity of the program and ensuring accurate output is generated.
Nested Loops
Nested loops occur when a loop operates inside another loop. In the Java program at hand, nested loops are used to print out a hollow square made of asterisks. The outer loop manages the rows of the square while the inner loop handles the columns within each row.

Here's how nested loops contribute in printing a square:
  • The outer loop runs from the first to the last row of the square.
  • Within each outer loop iteration, the inner loop prints an asterisk, followed by the appropriate number of spaces, and another asterisk for rows that are not the first or last.
  • For the first and last rows, the inner loop prints only asterisks to complete the top and bottom of the square.
Nested loops are powerful but can be complex, making it essential to understand their logic to maintain the program and use resources efficiently. They are particularly useful for tasks that require repetitively processing items in a multidimensional structure, such as a two-dimensional square.

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Most popular questions from this chapter

Explain what happens when a Java program attempts to divide one integer by another. What happens to the fractional part of the calculation? How can you avoid that outcome?

Write an application that reads three nonzero integers and determines and prints whether they could represent the sides of a right triangle.

(Find the Largest Number) The process of finding the largest value is used frequently in computer applications. For example, a program that determines the winner of a sales contest would input the number of units sold by cach salesperson. The salesperson who sells the most units wins the contest. Write a pseudocode program, then a Java application that inputs a series of 10 integers and determines and prints the largest integer. Your program should use at least the following three variables: a) counter: A counter to count to 10 (i.e., to keep track of how many numbers have been input and to determine when all 10 numbers have been processed). b) number: The integer most recently input by the user. c) Targest: The largest number found so far.

Fill in the blanks in each of the following statements: a) All programs can be written in terms of three types of control structures: ________, ________ and _______. b) The ________ statement is used to execute one action when a condition is true and another when that condition is false. c) Repeating a set of instructions a specific number of times is called ______ repetition. d) When it's not known in advance how many times a set of statements will be repeated, \(a(n)\) ______ value can be used to terminate the repetition. e) The _______ structure is built into Java; by default, statements execute in the order they appear. f) Instance variables of types char, byte, short, int, long, float and double are all given the value _______ by default. g) Java is a(n) ______ language; it requires all variables to have a type. h) If the increment operator is _______ to a variable, first the variable is incremented by \(1,\) then its new value is used in the expression.

(Checkerboard Pattern of Asterisks) Write an application that uses only the output statements System.out.print( \(" \pm \cdots)\) System.out.print( " " ) ; System.out.println(): to display the checkerboard pattern that follows. A System.out.println method call with no arguments causes the program to output a single newline character. [Hint: Repetition statements are required.
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