如何转置数组但不更改 c 中的行数和列数？

Question

I have recently encountered a problem in 2d array for which I am not able to get right solution. There's an array like:

    1,4,7,10,
    2,5,8,11,
    3,6,9,12

And I want it to be like:

    1,2,3,4,
    5,6,7,8,
    9,10,11,12

Heres a code snippet that I have written:

#include <stdio.h>    
int main ()    
{    
    
    int arr[3][4]={
        {1,4,7,10},
        {2,5,8,11},
        {3,6,9,12}
    };     
    
    int i,j;
    
    for(i=0;i<3;i++)
    {
        for(j=0;j<4;j++)
        {
            printf("%d ",arr[i][j]);
        }
        printf("\n");
    }
    
    printf("\n\n");
    int copy[3][4];
    int temp[3][4];
    
    for(i=0;i<3;i++)
    {
        for(j=0;j<4;j++)
        {
           copy[][]
        }
        
    }
    
    for(i=0;i<3;i++)
    {
        for(j=0;j<4;j++)
        {
            printf("%d ",copy[i][j]);
        }
        printf("\n");
    }
    return 0;
}    

Answer 1

The matrix

    1,4,7,10,
    2,5,8,11,
    3,6,9,12

can be written as

0*3+1, 1*3+1, 2*3+1, 3*3+1
0*3+2, 1*3+2, 2*3+2, 3*3+2
0*3+3, 1*3+3, 2*3+3, 3*3+3

On the other hand, the matrix

    1,2,3,4,
    5,6,7,8,
    9,10,11,12

can be written as

0*4+1, 0*4+2, 0*4+3, 0*4+4
1*4+1, 1*4+2, 1*4+3, 1*4+4
2*4+1, 2*4+2, 2*4+3, 2*4+4

Now it seems clearer. Then calculate the source and desitination coordinates and do assignments.

for(i=0;i<4*3;i++)
{
    int src_y=i%3, src_x=i/3, dst_y=i/4, dst_x=i%4;
    copy[dst_y][dst_x]=arr[src_y][src_x];
}