poj 1195 Mobile phones

#include<cstdio>
#include<cstring>
const int maxn=1024+5;
int s[maxn][maxn];
int n;
int lowbit(int x)
{
    return x&-x;
}
long long sum(int x,int y)
{
    long long  ret=0;
    for(int i=x;i>0;i-=lowbit(i))
        for(int j=y;j>0;j-=lowbit(j))
        ret+=s[i][j];
    return ret;
}
void add(int x,int y,int inc)
{
   for(int i=x;i<=n;i+=lowbit(i))
    for(int j=y;j<=n;j+=lowbit(j))
     s[i][j]+=inc;
}
int main()
{
        int com;
        int a,b,c,d;
        while(scanf("%d",&com)&&com!=3)
        {
            if(com==0)
            {
                scanf("%d",&n);
                memset(s,0,sizeof(s));
            }
            else if(com==1)
            {
                scanf("%d%d%d",&a,&b,&c);
                add(a+1,b+1,c);
            }
            else if(com==2)
            {
                scanf("%d%d%d%d",&a,&b,&c,&d);
                long long  ans=sum(c+1,d+1)+sum(a,b)-sum(c+1,b)-sum(a,d+1);
                printf("%lld
",ans);
            }
        }
    return 0;
}