qqq.c

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


void foo(double *output) {
    for(int i = 0; i < 10; ++i)
        output[i] = i;
}


int main(int argc, char *argv[])
{
    double arr[10];
    foo(arr);

    for(int i = 0; i < 10; ++i)
        printf("%f\n", arr[i]);

    return 0;
}