Flip matrix across its diagonal [closed] - c++

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What would be the simplest way to reorder my number values in the second matrix with 90 being in the top left and 10 being in the bottom right? My brain is going blank and I know there has to be any easy way to go about this. Any help is appreciated tremendously!
Here's what I'm trying to achieve.
#include <iostream>
using namespace std;
void main() {
cout << "Before:" << endl;
for (int i = 0; i < 9; i++) {
for (int j = 0; j < 9; j++) {
int matrix[9][9] = {
{ 10,11,12,13,14,15,16,17,18 },
{ 19,20,21,22,23,24,25,26,27,},
{ 28,29,30,31,32,33,34,35,36 },
{ 37,38,39,40,41,42,43,44,45 },
{ 46,47,48,49,50,51,52,53,54 },
{ 55,56,57,58,59,60,61,62,63 },
{ 64,65,66,67,68,69,70,71,72 },
{ 73,74,75,76,77,78,79,80,81 },
{ 82,83,84,85,86,87,88,89,90 }
};
cout << matrix[i][j] << " ";
}
cout << endl;
}
cout << "After:" << endl;
for (int i = 0; i < 9; i++) {
for (int j = 0; j < 9; j++) {
int transMatrix[9][9] = {
{ 10,11,12,13,14,15,16,17,18 },
{ 19,20,21,22,23,24,25,26,27,},
{ 28,29,30,31,32,33,34,35,36 },
{ 37,38,39,40,41,42,43,44,45 },
{ 46,47,48,49,50,51,52,53,54 },
{ 55,56,57,58,59,60,61,62,63 },
{ 64,65,66,67,68,69,70,71,72 },
{ 73,74,75,76,77,78,79,80,81 },
{ 82,83,84,85,86,87,88,89,90 }
};
cout << transMatrix[j][i] << " ";
}
cout << endl;
}
}

Answer 1

You could just loop in reverese.
for (int i = 8; i >= 0; i--) {
for (int j = 8; j >= 0; j--) {
//Print element [j][i] here
}
}
Also move the matrix assignment to outside of the loop as pointed out by Federico

Answer 2

Let's consider the following matrix
#define ROW 3
#define COL 4
int main()
{
int mat [ROW][COL] = {
{1, 2, 3, 4},
{5, 6, 7, 8},
{9, 10, 11, 12}
};
//...
return 0;
}
1/ If you want the backwards matrix
int backwards_mat[ROW][COL];
for(size_t i = 0; i < ROW; ++i)
{
for(size_t j = 0; j < COL; ++j)
{
backwards_mat[i][j] = mat[ROW-1-i][COL-1-j];
}
}
2/ If you want the transposed matrix
int transposed_mat[COL][ROW]; //swap the dimensions
for(size_t i = 0; i < ROW; ++i)
{
for(size_t j = 0; j < COL; ++j)
{
transposed_mat[j][i] = mat[i][j];
}
}
If you prints the two matrices, the backwards will be:
12 11 10 9
8 7 6 5
4 3 2 1
And the transposed will be:
1 5 9
2 6 10
3 7 11
4 8 12
You should be able to easily apply this to your matrix.

Answer 3

Do you mean the following?
#include <iostream>
#include <utility>
int main()
{
const size_t N = 9;
int matrix[N][N] =
{
{ 10,11,12,13,14,15,16,17,18 },
{ 19,20,21,22,23,24,25,26,27,},
{ 28,29,30,31,32,33,34,35,36 },
{ 37,38,39,40,41,42,43,44,45 },
{ 46,47,48,49,50,51,52,53,54 },
{ 55,56,57,58,59,60,61,62,63 },
{ 64,65,66,67,68,69,70,71,72 },
{ 73,74,75,76,77,78,79,80,81 },
{ 82,83,84,85,86,87,88,89,90 }
};
for ( const auto &row : matrix )
{
for ( const auto &item : row ) std::cout << item << ' ';
std::cout << '\n';
}
std::cout << '\n';
for ( size_t i = 0; i < N; i++ )
{
for ( size_t j = 0; j < N - i - 1; j++ ) std::swap( matrix[i][j], matrix[N-j-1][N-i-1] );
}
for ( const auto &row : matrix )
{
for ( const auto &item : row ) std::cout << item << ' ';
std::cout << '\n';
}
std::cout << '\n';
}
The program output is
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
46 47 48 49 50 51 52 53 54
55 56 57 58 59 60 61 62 63
64 65 66 67 68 69 70 71 72
73 74 75 76 77 78 79 80 81
82 83 84 85 86 87 88 89 90
90 81 72 63 54 45 36 27 18
89 80 71 62 53 44 35 26 17
88 79 70 61 52 43 34 25 16
87 78 69 60 51 42 33 24 15
86 77 68 59 50 41 32 23 14
85 76 67 58 49 40 31 22 13
84 75 66 57 48 39 30 21 12
83 74 65 56 47 38 29 20 11
82 73 64 55 46 37 28 19 10