Question

How to convert a 1D coordinate into 2D indexes in C++

Answer 1

#include <iostream>

int main(void)
{
    int array2d[4][5] = { { 1,   2,   3,   6,  0},
                          {-5,  -4,   0,   7,  9},
                          { 1,  18, 100,  14,  6},
                          { 9,  10,  27,  12, 13} };
  
    int array1d[] = { 1, 2, 3, 6, 0, -5, -4, 0, 7, 9, 1, 18, 100, 14, 6, 9, 10, 27, 12, 13 };
          
    int rows = (sizeof(array2d) / sizeof(array2d[0]));
    int cols = (sizeof(array2d) / sizeof(array2d[0][0])) / rows;
  
    int index = 17;
         
    // int i = 3, j = 2;
         
    int i = index / cols;
    int j = index - (i * cols); // index % cols;
 
    std::cout << "i = " << i << " j = " <<  j << "\n";
         
    std::cout << array1d[index] << "\n";  
    std::cout << array2d[i][j];   
}
  
 
  
/*
run:
  
i = 3 j = 2
27
27
 
*/

 

 

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