Question

I need to create a 375 x 375 grid in c, and I need to create a grid of 25 (5×5) poles that will be spaced 75 (375/5) grid points apart. I will then need to calculate for any given grid point how close it is to a pole. This is not a visual grid, but I’m still having trouble wrapping my head on how to create this grid set-up programmatically. So far, I’v created a “Point” struct that consist of two ints x and y:

typedef struct{
    int x, y;
}Point;

I then define my grid as a 375×375 Point array and set the x and y values asi and jrespectfully, in a nested for loop. However I’m having a hard time figuring out how to create the pole position array. Should it be a 5×5 array with the x and y values set as i*15 andj*15? If so then how would I use the two 2D arrays together.I couldn’t do a calculation like this obviously:

        for(i = 0; i < 375; i ++){
        for(j = 0; j<375; j++){
            distance(polePos[i][j], grid[i][j]);
        }
    }

but If I make it a 375×375 array, then how do I designate the pole position?
Am I on the right track? Any help would be appreciated.

Answer 1

You didn’t specify at which column-/row-indices the poles should be placed so in the following i place them 75-apart starting at 0, so the poles are at column-/row-indices 0, 75, 150, 225, 300, 375 (so 6 poles). It might not be precisely what you had in mind but it will get you started.

#include "stdio.h"
#include "math.h"
double distance(double x, double y, double grid) {
    x = fmod(x, grid);
    y = fmod(y, grid); // <- these modulos makes us treat every interval like the interval 0...grid
    double dx = grid/2 - fabs(x -grid/2);
    double dy = grid/2 - fabs(y -grid/2);    
    //printf("%3u %3u %f %f \n", x, y, dx, dy);
    return sqrt(dx*dx+dy*dy);
}
int main(void) {
    int i; int j;
    double grid[375][375];
      for(i = 0; i < 375; i ++){
        for(j = 0; j<375; j++){
            grid[i][j] = distance(i, j, 75);
            printf("%3u %3u %f\n", i, j, grid[i][j]);
        }
    }
}