Example: Alternating Rectangle Matrix in C

// Alternating Rectangle Matrix
#include <stdio.h>

void printMatrix(char matrix[100][100], int rows, int cols) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("%c ", matrix[i][j]);
        }
        printf("\n");
    }
}

int main() {
    int rows, cols;

    // Step 1: Get matrix dimensions from the user
    printf("Enter number of rows (max 100): ");
    scanf("%d", &rows);
    printf("Enter number of columns (max 100): ");
    scanf("%d", &cols);

    // Basic validation for dimensions
    if (rows <= 0 || cols <= 0 || rows > 100 || cols > 100) {
        printf("Invalid dimensions. Please enter positive numbers up to 100.\n");
        return 1;
    }

    // Step 2: Declare the matrix
    char matrix[100][100];

    // Step 3: Initialize boundary variables and fill character
    int top = 0;
    int bottom = rows - 1;
    int left = 0;
    int right = cols - 1;
    char fill_char = 'O'; // Start with 'O' for the outermost layer

    // Step 4: Loop to fill layers until boundaries cross
    while (top <= bottom && left <= right) {
        // Fill top row
        for (int i = left; i <= right; i++) {
            matrix[top][i] = fill_char;
        }
        top++; // Move top boundary inwards

        // Fill right column
        for (int i = top; i <= bottom; i++) {
            matrix[i][right] = fill_char;
        }
        right--; // Move right boundary inwards

        // Fill bottom row (only if valid row exists)
        if (top <= bottom) {
            for (int i = right; i >= left; i--) {
                matrix[bottom][i] = fill_char;
            }
            bottom--; // Move bottom boundary inwards
        }

        // Fill left column (only if valid column exists)
        if (left <= right) {
            for (int i = bottom; i >= top; i--) {
                matrix[i][left] = fill_char;
            }
            left++; // Move left boundary inwards
        }

        // Switch character for the next layer
        fill_char = (fill_char == 'O') ? 'X' : 'O';
    }

    // Step 5: Print the resulting matrix
    printf("\nGenerated Matrix:\n");
    printMatrix(matrix, rows, cols);

    return 0;
}