C++ Program to Interchange elements of first and last rows in matrix

Last Updated : 21 Aug, 2026

Given a matrix, the task is to interchange its first and last rows. This can be done by swapping the corresponding elements of the first and last rows.

  • Swap each element of the first row with the corresponding element of the last row.
  • The operation can be performed in-place using constant extra space.

Example

Input:

3 4 5 0
2 6 1 2
2 7 1 2
2 1 1 2

Output:

2 1 1 2
2 6 1 2
2 7 1 2
3 4 5 0

Approach

The first and last rows have the same number of elements. Traverse all columns and swap the corresponding elements of these two rows.

  • Traverse each column of the matrix.
  • Swap the element at the first row with the element at the last row.
  • Print the updated matrix.
C++ 
#include <iostream>
using namespace std;

const int N = 4;

// Interchange first and last rows
void interchangeFirstLast(int mat[N][N])
{
    for (int j = 0; j < N; j++) {
        swap(mat[0][j], mat[N - 1][j]);
    }
}

int main()
{
    int mat[N][N] = {
        {8, 9, 7, 6},
        {4, 7, 6, 5},
        {3, 2, 1, 8},
        {9, 9, 7, 7}
    };

    interchangeFirstLast(mat);

    // Print the updated matrix
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            cout << mat[i][j] << " ";
        }
        cout << '\n';
    }

    return 0;
}

Output
9 9 7 7 
4 7 6 5 
3 2 1 8 
8 9 7 6

Explanation

  • The loop traverses all columns of the matrix.
  • swap() exchanges the corresponding elements of the first and last rows.
  • The matrix is modified directly without using another matrix.
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