Question

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

Answer 1

#include <stdio.h>
 
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;

    printf("i = %d j = %d\n", i, j);
        
    printf("%d\n", array1d[index]);  
    printf("%d\n", array2d[i][j]);   

    return 0;
}
 

 
/*
run:
 
i = 3 j = 2
27
27

*/

 

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