How can I reverse a each column of a matrix - c++

Question

I want to change the a matrix
A=[[1,2],[3,4]] to A'=[[3,4],[1,2]]
How can I write a C++ program to make this change
Here is my attempt. but it fails
Here I am declaring a global variable g=0
and at each iteration I am trying to reverse each row
#include<bits/stdc++.h>
using namespace std;
int g=0;
void rotaterow(vector<vector<int>>&matrix, int a, int j)
{
int n = matrix.size();
int k=n-1;
for (int i = 0; i < n/2; i++)
{
int s=matrix[a][g];
int b=matrix[k][g];
swap(matrix[a][i], matrix[k--][j]);
}
g++;// taking g as a global variable
//matrix[a][n - 1] = temp;
}
int main()
{
int n;
cin>>n;
vector<vector<int>>matrix(n, vector<int>(n));
for(int i=0;i<n;i++)
{
for(int j=0;j<n;j++)
{
cin>>matrix[i][j];
}
}
for(int j=0;j<n;j++)
rotaterow(matrix,0,j);
for(int i=0;i<n;i++)
{
for(int j=0;j<n;j++)
cout<<matrix[i][j]<<" ";
cout<<endl;
}
}

Answer 1

Since you didn't mention any specific problem with your program, you can use std::swap as shown below:
#include <vector>
#include <iostream>
int main()
{
std::vector<std::vector<int>> vec = {{1,2,3}, {4,5,6}};
std::cout<<"before swap: "<<std::endl;
for(std::vector<std::vector<int>>::size_type row = 0; row < vec.size(); ++row)
{
for(std::vector<int>::size_type col = 0; col < vec.at(row).size(); ++col)
{
std::cout<<vec.at(row).at(col)<<" ";
}
std::cout<<std::endl;
}
//swap the 0th and 1st column
std::swap(vec.at(0), vec.at(1));
std::cout<<"after swap: "<<std::endl;
for(std::vector<std::vector<int>>::size_type row = 0; row < vec.size(); ++row)
{
for(std::vector<int>::size_type col = 0; col < vec.at(row).size(); ++col)
{
std::cout<<vec.at(row).at(col)<<" ";
}
std::cout<<std::endl;
}
}
The output of the above program can be seen here.