3D array indexing.

arr.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#include <assert.h>


int main(int argc, char* argv[]) {
    int idim = 3;
    int jdim = 4;
    int kdim = 5;
    int footprint = idim*jdim*kdim;
    int *arr = malloc( footprint * sizeof(int));
    int *mini;

    for (int i = 0; i < footprint; i++) {
        arr[i] = i;
    }

    for (int i = 0; i < idim; i++) {
        for (int j = 0; j < jdim; j++) {
            for (int k = 0; k < kdim; k++) {
                int idx = i*(jdim*kdim) + j * (kdim) + k;
                assert(idx < footprint);
                printf("%2i ", arr[idx]);
            }
            printf("\n");
        }
        printf("\n");
    }

    int slice = 2;
    int row = 2;

    mini = arr + (slice*(jdim*kdim)) + row*(kdim);

    printf("\n");
    printf("Slice %i, Row %i\n", slice, row);
    for (int i = 0; i < kdim; ++i) {
        printf("%i ", mini[i]);
    }
    printf("\n");


    return 0;
}