C++ Program To Display Box Shape Using For Loop

Looping constructs are fundamental in programming for repetitive tasks, such as generating patterns and shapes on the console. In C++, for loops are particularly effective for such graphical outputs. In this article, you will learn how to create a C++ program to display various box shapes using for loops.

Problem Statement

The challenge is to programmatically display a rectangular box shape on the console, given specific dimensions for its width and height. This involves arranging characters like asterisks (*) and spaces in a grid-like fashion to form either an empty outline or a solid, filled box.

Example

Consider a box with a width of 5 and a height of 4.

*****
*   *
*   *
*****

Background & Knowledge Prerequisites

To understand and implement the solutions in this article, readers should have a basic understanding of the following C++ concepts:

• Variables: Declaring and initializing integer variables.
• for Loops: Understanding how to use nested for loops for iteration.
• Conditional Statements: Using if and else for decision-making.
• Standard I/O: Using std::cout for printing output and std::cin for taking user input.

Use Cases or Case Studies

Creating console-based patterns and shapes, like boxes, has several practical applications:

• Simple Console UI: Designing basic user interface elements or borders in text-based applications.
• Game Development (Text-based): Representing game board boundaries, walls, or obstacles in simple text-based games.
• Educational Tools: Illustrating fundamental programming concepts like loops, nested loops, and conditional logic.
• Data Visualization: Creating rudimentary visual representations of data structures or grids in a console environment.
• Debugging/Logging: Visually separating sections in logs or debugging output for better readability.

Solution Approaches

We will explore two common approaches to display box shapes: a box outline and a filled box.

Approach 1: Display a Box Outline

This approach focuses on drawing only the perimeter of the box, leaving the interior empty.

One-line summary: Use nested for loops with conditional logic to print asterisks only for the first row, last row, first column, and last column, otherwise print spaces.

// Box Outline
#include <iostream>
using namespace std;

int main() {
    int width, height;

    // Step 1: Get dimensions from the user
    cout << "Enter the width of the box: ";
    cin >> width;
    cout << "Enter the height of the box: ";
    cin >> height;

    // Step 2: Iterate through each row
    for (int i = 1; i <= height; ++i) {
        // Step 3: Iterate through each column in the current row
        for (int j = 1; j <= width; ++j) {
            // Step 4: Check if current position is part of the border
            if (i == 1 || i == height || j == 1 || j == width) {
                cout << "*"; // Print asterisk for border
            } else {
                cout << " "; // Print space for interior
            }
        }
        cout << endl; // Move to the next line after each row
    }

    return 0;
}

Run

Sample Output:

Enter the width of the box: 7
Enter the height of the box: 5
*******
*     *
*     *
*     *
*******

Stepwise Explanation:

1. Get Dimensions: The program prompts the user to input the desired width and height for the box.
2. Outer Loop (Rows): An outer for loop iterates from i = 1 to height. Each iteration represents a new row of the box.
3. Inner Loop (Columns): An inner for loop iterates from j = 1 to width. Each iteration represents a position within the current row.
4. Conditional Printing: Inside the inner loop, an if statement checks the current position (i, j):
   • If i is the first row (i == 1) or the last row (i == height), it's a horizontal border.

1. Newline: After each complete row (inner loop finishes), cout << endl; moves the cursor to the next line, ensuring the box is drawn vertically.

Approach 2: Display a Filled Box

This approach displays a solid box, where every position inside the defined dimensions is filled with a character.

One-line summary: Use simple nested for loops to print an asterisk for every cell in the grid defined by the given width and height.

// Filled Box
#include <iostream>
using namespace std;

int main() {
    int width, height;

    // Step 1: Get dimensions from the user
    cout << "Enter the width of the filled box: ";
    cin >> width;
    cout << "Enter the height of the filled box: ";
    cin >> height;

    // Step 2: Iterate through each row
    for (int i = 0; i < height; ++i) {
        // Step 3: Iterate through each column in the current row
        for (int j = 0; j < width; ++j) {
            cout << "*"; // Print asterisk for every position
        }
        cout << endl; // Move to the next line after each row
    }

    return 0;
}

Run

Sample Output:

Enter the width of the filled box: 6
Enter the height of the filled box: 3
******
******
******

Stepwise Explanation:

1. Get Dimensions: Similar to the previous approach, the program takes width and height input from the user.
2. Outer Loop (Rows): An outer for loop iterates from i = 0 to height - 1. This controls the number of rows.
3. Inner Loop (Columns): An inner for loop iterates from j = 0 to width - 1. This controls the number of characters in each row.
4. Unconditional Printing: Unlike the outline approach, there's no if statement. An asterisk (*) is printed for every position in the grid.
5. Newline: After each inner loop completes, cout << endl; ensures that the next set of asterisks starts on a new line, forming the vertical structure of the box.

Conclusion

Using for loops, specifically nested for loops, provides a powerful and flexible way to generate various patterns and shapes on the console in C++. By applying simple conditional logic within these loops, you can precisely control which characters are printed at each position, allowing for the creation of intricate designs like box outlines and solid filled boxes. These fundamental techniques are essential building blocks for more complex console-based graphics and pattern recognition tasks.

Summary

• Nested for loops are crucial for iterating over rows and columns to draw 2D patterns.
• Conditional statements (if/else) within loops enable differentiation between border and interior elements for patterns like box outlines.
• Without conditions, nested loops can easily create solid, filled shapes.
• Input from the user (std::cin) allows for dynamic sizing of the patterns.
• std::cout << endl; is vital for moving to a new line after each row to form the vertical structure of the pattern.