C program to swap the rows-to-columns for any square matrix

This is essentially asking for a transpose of a square matrix (rows become columns and vice versa). Below is a simple program to implement this problem,

#include <stdio.h>

#define MAX 10  // maximum size of the matrix

// Function to print the matrix
void printMatrix(int matrix[MAX][MAX], int n) {
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            printf("%d\t", matrix[i][j]);
        }
        printf("\n");
    }
}

int main() {
    int n;
    int matrix[MAX][MAX];

    printf("Enter the size of the square matrix (n x n): ");
    scanf("%d", &n);

    if (n > MAX) {
        printf("Error: Maximum size allowed is %d\n", MAX);
        return 1;
    }

    printf("Enter the elements of the %d x %d matrix:\n", n, n);
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            scanf("%d", &matrix[i][j]);
        }
    }

    printf("\nOriginal Matrix:\n");
    printMatrix(matrix, n);

    // Transpose in place (swap rows and columns)
    for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            int temp = matrix[i][j];
            matrix[i][j] = matrix[j][i];
            matrix[j][i] = temp;
        }
    }

    printf("\nMatrix after swapping rows to columns (Transpose):\n");
    printMatrix(matrix, n);

    return 0;
}

Code Walkthrough

1. The user enters the size n and the n x n matrix.
2. We print the original matrix.
3. To transpose: for each pair (i, j) above the diagonal, we swap matrix[i] with matrix[j].
4. This avoids double-swapping and keeps the diagonal elements unchanged.
5. Finally, we print the transposed matrix.