在C++中 double会以牺牲最小数为代价换取高位

另外请看好题目是求整数部分还是四舍五入

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<cctype>
#include<iostream>
#include<functional>
#include<algorithm>
#include<string>
using namespace std;
#define MAXN (1000+10)
int a[MAXN][MAXN],n;
int main()
{
	long double ans=0.0;
	scanf("%d",&n);
	long long all=0;
	for (int i=1;i<=n;i++)
	{
		for (int j=1;j<=n;j++)
			all+=((long long)n-i+1)*((long long)n-j+1);
	}

	for (int i=1;i<=n;i++)
		for (int j=1;j<=n;j++)
	{
		scanf("%d",&a[i][j]);
		ans+=(long double)(a[i][j])*(long double)(n-i+1)*(long double)(n-j+1)*(long double)(i*j);

	//	cout<<ans<<' ';
	}

	cout.setf(ios::fixed);
	cout.precision(0);
	cout<<trunc(ans/(long double)(all))<<endl;



	return 0;
}