C Program To Display Box Shape Using For Loop

Creating visual patterns in C often involves using loops to control character placement. In this article, you will learn how to display a simple box shape using for loops, a fundamental concept in programming.

Problem Statement

The challenge is to print a rectangular box composed of characters to the console. This requires carefully controlling where characters like '*' or '#' are printed to form the outline and fill of the box, ensuring correct dimensions and character placement.

Example

Here's an example of a 7x4 box (7 columns, 4 rows) that we aim to create:

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

Background & Knowledge Prerequisites

To effectively follow this article, readers should have a basic understanding of:

• C Language Basics: Variables, data types, main function.
• printf() function: For outputting text to the console.
• for loops: How to initialize, set conditions, and increment/decrement loop counters, including nested for loops.

Use Cases or Case Studies

Creating character-based shapes using loops has several practical applications, especially in environments where graphical interfaces are not available or desired:

• Text-Based User Interfaces (TUIs): Developing simple menus, dialog boxes, or layouts for console applications.
• Simple Game Graphics: Crafting basic game elements like walls, obstacles, or player boundaries in text-based adventure games.
• Console-Based Drawing Tools: Building rudimentary tools that allow users to draw shapes using keyboard inputs.
• Debugging and Visualization: Visualizing data structures or program flow in a simple, character-based format during development.
• Educational Purposes: Teaching fundamental programming concepts like loops, conditional statements, and algorithmic thinking through visual output.

Solution Approaches

We will explore two main approaches for drawing a box: first with fixed dimensions, then with user-defined dimensions, building on the same core for loop logic.

Approach 1: Basic Box with Fixed Dimensions

This approach uses hardcoded width and height values to draw a box. It's a great way to understand the core logic before introducing user input.

• Summary: Uses nested for loops to iterate through rows and columns, printing '*' for borders and ' ' (space) for the interior.

// Basic Box with Fixed Dimensions
#include <stdio.h>

int main() {
    // Step 1: Define box dimensions
    int width = 7;
    int height = 4;

    // Step 2: Loop through each row
    for (int i = 1; i <= height; i++) {
        // Step 3: Loop 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) {
                printf("*"); // Print asterisk for border
            } else {
                printf(" "); // Print space for interior
            }
        }
        printf("\\n"); // Move to the next line after each row
    }

    return 0;
}

Run

• Sample Output:

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

• Stepwise Explanation:

1. Define Dimensions: width and height variables are set to determine the size of the box.
2. Outer Loop (Rows): The first for loop iterates from i = 1 to height. Each iteration represents one row of the box.
3. Inner Loop (Columns): Nested inside, the second for loop iterates from j = 1 to width. Each iteration represents one character position within the current row.
4. Border Condition: Inside the inner loop, an if statement checks if the current position (i, j) is on the top row (i == 1), bottom row (i == height), left column (j == 1), or right column (j == width).
5. Print Characters:

• If the condition is true (it's a border position), printf("*") prints an asterisk.
• Otherwise (it's an interior position), printf(" ") prints a space.

1. Newline: After the inner loop completes (a full row has been printed), printf("\n") moves the cursor to the next line, preparing for the next row.

Approach 2: Box with User-Defined Dimensions

This approach enhances the previous one by allowing the user to specify the width and height of the box at runtime.

• Summary: Prompts the user for box dimensions, then uses the same nested for loop logic as Approach 1 to draw the box based on user input. Includes basic input validation.

// Box with User-Defined Dimensions
#include <stdio.h>

int main() {
    // Step 1: Declare variables for width and height
    int width, height;

    // Step 2: Prompt user for dimensions and read input
    printf("Enter the width of the box: ");
    scanf("%d", &width);
    printf("Enter the height of the box: ");
    scanf("%d", &height);

    // Step 3: Validate input to ensure reasonable dimensions
    if (width < 3 || height < 3) { // Minimum size for a recognizable box
        printf("Dimensions must be at least 3 for a proper box outline.\\n");
        return 1; // Indicate an error
    }

    // Step 4: Loop through each row
    for (int i = 1; i <= height; i++) {
        // Step 5: Loop through each column in the current row
        for (int j = 1; j <= width; j++) {
            // Step 6: Check if current position is part of the border
            if (i == 1 || i == height || j == 1 || j == width) {
                printf("*"); // Print asterisk for border
            } else {
                printf(" "); // Print space for interior
            }
        }
        printf("\\n"); // Move to the next line after each row
    }

    return 0;
}

Run

• Sample Output (User enters width = 10, height = 5):

Enter the width of the box: 10
Enter the height of the box: 5
**********
*        *
*        *
*        *
**********

• Stepwise Explanation:

1. Declare Variables: width and height are declared to store the user's input.
2. Get User Input: printf() prompts the user, and scanf() reads the integer values for width and height from the console.
3. Input Validation: An if statement checks if the entered width or height is less than 3. A box needs at least 3 units in each dimension (top, middle, bottom and left, middle, right) to display a clear outline. If dimensions are too small, an error message is printed, and the program exits.
4. Drawing Logic: The rest of the logic (for loops and if condition for printing characters) is identical to Approach 1, but it now uses the width and height values provided by the user.

Conclusion

Creating a box shape in C using for loops is a fundamental exercise that demonstrates control flow, nested loops, and conditional logic. By carefully checking the current row and column indices, you can determine whether to print a border character or an interior space, allowing for flexible and scalable pattern generation.

Summary

• Nested for loops are essential for iterating through rows and columns to build two-dimensional patterns.
• Conditional statements (if/else) within the loops are used to decide which character to print based on the position (e.g., border or interior).
• Input validation is crucial when accepting user input to ensure the program behaves correctly and produces meaningful output.
• This technique forms the basis for more complex text-based graphical applications and helps solidify understanding of basic programming constructs.