//this is mergesort version of tham tro / tham bien
#include<stdio.h>
// start array with index 0 (l=0,r=number elements of array -1)
void mergesort(int *a,int l,int r){
    int i,j,k,m;
    int *b,*c;
    if(r-l>0) {
        m=(r+l)/2;
        mergesort(a,l,m);
        mergesort(a,m+1,r);
        for (int i = m; i >= l; i--)
            *(b+i)=*(a+i);  //how to use reference parameter to return in void methods
        for (int j = m+1; j <= r; j++)
            *(c+i)=*(a+i);
        i=0;
        j=0;
        for (int k = 0; k <= r; k++) {
            if(*(b+i)<*(c+i))
                *(a+k) = *(b+(i++));
            else
                *(a+k) = *(c+(j++));
        }
    }
}
int main(int argc, char const *argv[])
{
    int a[8] = {5,4,1,8,7,2,6,3};
    mergesort(a,0,7);
    for (int i = 0; i < 7; i++)
    {
        printf("%d\n", a[i]);
        /* code */
    }
    return 0;
}