Question

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 berween 1 and 20 .

Short answer

Write a program that reads a side length and prints a hollow square of that size using loops.

Step-by-step solution

Understand the Problem

The problem requires creating a program that prompts the user to enter the size of a square's side, and then displays a hollow square made of asterisks. The side length should be between 1 and 20.

Plan the Logic of the Program

To create a hollow square, two solid rows (the first and the last) of asterisks are needed. Between these rows, the interior rows should have asterisks only at the beginning and the end, with spaces in between. All rows should have the same number of characters as the side length.

Handle Input

Use input functions to prompt the user to enter an integer representing the side length of the square. Convert this input to an integer type and check that it is between 1 and 20. If not, prompt again until a valid input is received.

Generate the Square Pattern

Use a loop to iterate over a range equal to the side length. For the first and last indices, print an entire row of asterisks. For other indices, print an asterisk, then spaces, and finally another asterisk, ensuring the total characters equal the side length.

Output the Result

Display the generated square pattern on the screen. Ensure the output matches the expected hollow square of asterisks, reflecting the side length chosen by the user.

Key concepts

Loops

In Java programming, loops allow you to execute a block of code repeatedly. One common loop is the "for loop," especially handy when you know how many times you need to repeat the code.
For the hollow square problem, a loop can iterate over each row of the square.

• Create a loop that runs from 1 to the side length of the square.
• For the first and last iteration, print a full row of asterisks.
• For the iterations in between, print an asterisk, then spaces, and finally another asterisk.

By using loops, you efficiently manage repeating tasks without writing redundant code.

User Input

Taking user input is essential when creating interactive programs. In Java, the `Scanner` class is frequently used to receive input from the user.
Setting it up involves a few steps:

• Import the Scanner class using `import java.util.Scanner;`.
• Create a new Scanner object, typically named 'input' or 'scanner'.
• Prompt the user to enter data, then use methods like `nextInt()` to retrieve it.

This approach allows the program to operate based on user-provided data, making it adaptable to different inputs.

Conditional Statements

Conditional statements are crucial for decision-making in code. In our exercise, they determine when to print spaces or asterisks.
Using constructs like `if` and `else`, we can specify:

• Whether to print a full row of asterisks (for the first and last rows).
• When to print only the beginning and end asterisks, plus spaces in between (for the interior rows).

These conditions ensure the right parts of the square are drawn correctly, forming the hollow structure.

Iteration

Iteration involves executing code multiple times, and loops are a primary tool for this in Java.
In the hollow square task, iteration is used to move through each line from top to bottom.
We iterate over each row and column within that row:

• Outer loop iterates over rows (number of iterations = side length).
• Inner logic checks each column within the current row.

This repeated action allows you to build a complex structure, like the hollow square, piece by piece.

Output Formatting

Output formatting ensures the program presents information in a readable and organized manner. In a text-based pattern like the hollow square, alignment is key.
Some essential steps include:

• Ensuring each line of output is precise and matches the expected pattern.
• Using the correct number of spaces and characters for alignment.
• Checking that no extra characters or spaces disrupt the visual structure.

Proper formatting makes it easier for users to understand and inspect the output, particularly in structured patterns.