Ultra-QuickSort POJ - 2299 Fenwick tree seeking to reverse

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
typedef long long ll;
const int N=5e5+10;
int n;
int a[N];
int tr[N];
int b[N];
int c[N]; 
int lowbit(int x)
{
    return x&-x;
}
void add(int x,int c)
{
    for(int i=x;i<=n;i+=lowbit(i))
        tr[i]+=c;
}
int sum(int x)
{
    int res=0;
    for(int i=x;i;i-=lowbit(i))
        res+=tr[i];
    return res;
}
int main()
{
    while(cin>>n,n)
    {
        for(int i=1;i<=n;i++)
        {
            cin>>a[i];
            b[i]=A [I]; 
        } 
        // end position 
        Sort (b + . 1 , b + . 1 + n-);
         // A positions of the elements in the b, c, then placed 
         // A 1 ~ n elements should be in a position 
        
        // equivalent discretized 
        for ( int I = . 1 ; I <= n-; I ++ ) 
            C [I] = lower_bound (B + . 1 , B + . 1 + n-, A [I]) - B; 
        Memset (TR, 0 , the sizeof TR); 
        LL ANS = 0 ;
         for ( int I = . 1 ; I <= n-; I ++)
        {
            add(c[i],1);
            ans+=i-sum(c[i]);
        } 
        cout<<ans<<endl;
    }
}