``````/*************************************************
** This program reads in points from the user and
** prints them back out in sorted order from
** closest to the origin to farthest.
*************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/*************************************************
** PROTOTYPES
*************************************************/
void selectionSort(double** data, int size);

/*************************************************
** MAIN
*************************************************/
int main() {
// Get number of points and create & read array
int n;
printf("How many points? ");
fflush(stdout);
scanf(" %d", &n);
printf("Enter points (x,y,z): ");
fflush(stdout);

double** points = calloc(n, sizeof(double*));
for(int i = 0; i < n; i++) {
points[i] = calloc(3, sizeof(double));
scanf(" ( %lg , %lg , %lg )", &points[i][0], &points[i][1], &points[i][2]);
}

// Sort points!
selectionSort(points, n);

// Print out points
for(int i = 0; i < n; i++) {
printf("(%g,%g,%g) ", points[i][0], points[i][1], points[i][2]);
}
printf("\n");

// clean up
for (int i=0; i < n; ++i) {
free(points[i]);
}
free(points);

return 0;
}

/*************************************************
** DEFINITIONS
*************************************************/
int before(double* a, double* b) {
return sqrt(a[0]*a[0] + a[1]*a[1] + a[2]*a[2])
<
sqrt(b[0]*b[0] + b[1]*b[1] + b[2]*b[2]);
}

void selectionSort(double** data, int size) {
for(int length = size; length > 1; length--) {
// Find imax, the index of the largest
int imax = 0;
for(int i = 1; i < length; i++) {
if (before(data[imax], data[i])) {
imax = i;
}
}
// Swap data[imax] & the last element
double* temp = data[imax];
data[imax] = data[length - 1];
data[length - 1] = temp;
}
}``````