Example: Matrix Transpose Using Pointers in C

// Matrix Transpose Using Pointers
#include <stdio.h>

#define ROWS 2
#define COLS 3

void printMatrix(int *matrix, int rows, int cols) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            // Access element using pointer arithmetic: *(matrix + i * cols + j)
            printf("%d ", *(matrix + i * cols + j));
        }
        printf("\n");
    }
}

void transposeMatrix(int *original, int *transposed, int rows, int cols) {
    // Step 1: Iterate through rows of the original matrix
    for (int i = 0; i < rows; i++) {
        // Step 2: Iterate through columns of the original matrix
        for (int j = 0; j < cols; j++) {
            // Step 3: Calculate the memory address of the current element in the original matrix
            // For a 2D array treated as 1D, element (i, j) is at index (i * cols + j)
            int *original_element_ptr = original + (i * cols + j);
            
            // Step 4: Calculate the memory address for the transposed position in the new matrix
            // In the transposed matrix, original[i][j] becomes transposed[j][i].
            // For the transposed matrix (cols x rows), element (j, i) is at index (j * rows + i)
            int *transposed_element_ptr = transposed + (j * rows + i);
            
            // Step 5: Assign the value from the original matrix to the transposed matrix
            *transposed_element_ptr = *original_element_ptr;
        }
    }
}

int main() {
    int originalMatrix[ROWS][COLS] = {
        {1, 2, 3},
        {4, 5, 6}
    };
    
    // The transposed matrix will have COLS rows and ROWS columns
    int transposedMatrix[COLS][ROWS]; 

    printf("Original Matrix:\n");
    // Pass the base address of the 2D array to the function
    printMatrix((int *)originalMatrix, ROWS, COLS);

    // Call the transpose function, passing base addresses and dimensions
    transposeMatrix((int *)originalMatrix, (int *)transposedMatrix, ROWS, COLS);

    printf("\nTransposed Matrix:\n");
    // Print the transposed matrix (note dimensions are swapped for printMatrix)
    printMatrix((int *)transposedMatrix, COLS, ROWS);

    return 0;
}