printing stack in the incorrect order in c++ - c++

Question

I have a function that pushes down all non zero integers to the top of my array and then reprints it in a 3x3 matrix.
the problem i am having is when i push all the non zero integers into my stack it reverses the order.
** the indexing of my array is backwards. ie, in a 3x3 matrix the coordinates (0,0) would be the bottom left **
here is the relevant code:
void State::pushDown() {
std::stack<int> tempStack;
for ( int c = 0; c < BOARDSIZE; c++ )
{
for ( int r = 0; r < BOARDSIZE ; r++ )
{
if ( grid[r][c] != 0 ) tempStack.push( grid[r][c] );
}
for ( int r = BOARDSIZE; r != 0; --r )
{
if ( !tempStack.empty() )
{
grid[r-1][c] = tempStack.top();
tempStack.pop();
}
else
{
grid[r-1][c] = 0;
}
}
}
}
State() {
for (int i = 0; i < BOARDSIZE; i++)
for (int j = 0; j < BOARDSIZE; j++)
grid[i][j] = rand() % 7;
}
void State::printBoard() {
cout << endl;
for (int i = 0; i < BOARDSIZE; i++) {
for (int j = 0; j < BOARDSIZE; j++) {
cout << " " << grid[BOARDSIZE - i - 1][j] << " ";
}
cout << endl;
}
}
int main() {
srand(time(0));
State state;
state.printBoard();
state.pushDown();
state.printBoard();
return 0;
}
here is my current output:
before push down function
045
504
226
after push down function:
006
224
545
as you can see it successfully pushes the non zero elements to the bottom of the matrix however in the process it reverses the order of the other numbers and i believe this is because of the stack.
my expected output would be the following:
before push down function
045
504
226
after push down function:
005
544
226
My question is- how can i fix my function so that the order of the elements remain the same without reversing.

Answer 1

Here is a demonstrative program that shows how the loops can be defined.
#include <iostream>
#include <stack>
const int BOARDSIZE = 3;
void reformat( int ( &a )[BOARDSIZE][BOARDSIZE] )
{
std::stack<int> tempStack;
for ( int c = 0; c < BOARDSIZE; c++ )
{
for ( int r = 0; r < BOARDSIZE ; r++ )
{
if ( a[r][c] != 0 ) tempStack.push( a[r][c] );
}
for ( int r = BOARDSIZE; r != 0; --r )
{
if ( !tempStack.empty() )
{
a[r-1][c] = tempStack.top();
tempStack.pop();
}
else
{
a[r-1][c] = 0;
}
}
}
}
int main()
{
int a[BOARDSIZE][BOARDSIZE] =
{
{ 0, 4, 5 },
{ 5, 0, 4 },
{ 2, 2, 6 }
};
for ( const auto &row : a )
{
for ( const auto &item : row ) std::cout << item << ' ';
std::cout << '\n';
}
std::cout << '\n';
reformat( a );
for ( const auto &row : a )
{
for ( const auto &item : row ) std::cout << item << ' ';
std::cout << '\n';
}
std::cout << '\n';
return 0;
}
Its output is
0 4 5
5 0 4
2 2 6
0 0 5
5 4 4
2 2 6
If you are outputting the array starting from its last row then use the following loops
#include <iostream>
#include <stack>
const int BOARDSIZE = 3;
void reformat( int ( &a )[BOARDSIZE][BOARDSIZE] )
{
std::stack<int> tempStack;
for ( int c = 0; c < BOARDSIZE; c++ )
{
for ( int r = 0; r < BOARDSIZE ; r++ )
{
if ( a[BOARDSIZE-r-1][c] != 0 ) tempStack.push( a[BOARDSIZE-r-1][c] );
}
for ( int r = 0; r != BOARDSIZE; ++r )
{
if ( !tempStack.empty() )
{
a[r][c] = tempStack.top();
tempStack.pop();
}
else
{
a[r][c] = 0;
}
}
}
}
int main()
{
int a[BOARDSIZE][BOARDSIZE] =
{
{ 2, 2, 6 },
{ 5, 0, 4 },
{ 0, 4, 5 }
};
for ( size_t i = 0; i < BOARDSIZE; i++ )
{
for ( const auto &item : a[BOARDSIZE - i - 1] ) std::cout << item << ' ';
std::cout << '\n';
}
std::cout << '\n';
reformat( a );
for ( size_t i = 0; i < BOARDSIZE; i++ )
{
for ( const auto &item : a[BOARDSIZE - i - 1] ) std::cout << item << ' ';
std::cout << '\n';
}
std::cout << '\n';
return 0;
}
The program output is the same as shown above
0 4 5
5 0 4
2 2 6
0 0 5
5 4 4
2 2 6
But now the array is outputted starting from its last line.