10.付账问题

蓝桥杯 蓝桥杯第九届 C++ 贪心 所有文稿

/*16:13 start*/
#include <iostream>
#include <iomanip>
#include <cmath>
#include <algorithm>
using namespace std;
const int maxn=50000+10;
int a[maxn];
double b[maxn];
double bzc(int n){
    double tot_b=0.0,s0=0.0;
    for(int i=1;i<=n;i++){
        tot_b+=b[i];
    }
    tot_b=tot_b/(n*1.0);
    cout<<endl<<"tot_b="<<tot_b<<endl;
    for(int i=1;i<=n;i++){
        s0=s0+(b[i]-tot_b)*1.0*(b[i]-tot_b);
        cout<<"i="<<i<<" "<<(b[i]-tot_b)<<endl;
    }
    cout<<"s0="<<s0<<endl;
    return sqrt(s0/(1.0*n));
}
int main(){
    int n;
    double s;
    cin>>n>>s;
    for(int i=1;i<=n;i++) cin>>a[i];
    sort(a,a+n);
    double aver=s*1.0/n;
    int i=1;
    while(s>0){
        if (a[i]<aver) b[i]=a[i]*1.0;
        else b[i]=aver;
        s-=b[i];
        if (n>i){
        aver=s*1.0/(n-i);
        i++;}
    }
    for(int i=1;i<=n;i++) cout<<a[i]<<" ";
    cout<<endl;
    for(int i=1;i<=n;i++) cout<<b[i]<<" ";
    cout<<endl<<bzc(n)<<endl;
    double tot_b=0.0,s0=0.0;
    for(int i=1;i<=n;i++){
        tot_b+=b[i];
    }
    tot_b=tot_b/(n*1.0);
    cout<<endl<<"tot_b="<<tot_b<<endl;
    for(int i=1;i<=n;i++){
        s0=s0+(b[i]-tot_b)*1.0*(b[i]-tot_b);
        cout<<"i="<<i<<" "<<(b[i]-tot_b)<<endl;
    }
    cout<<"s0="<<sqrt(s0/(1.0*n))<<endl;
    system("pause");
    return 0;
}

出现了很神奇的输出结果

5 2333
666 666 666 666 666
666 666 666 666 666
466.6 466.6 466.6 466.6 466.6
tot_b=466.6
i=1 0
i=2 0
i=3 5.68434e-014
i=4 0
i=5 0
s0=3.23117e-027
2.54211e-014
tot_b=466.6
i=1 0
i=2 0
i=3 5.68434e-014
i=4 0
i=5 0
s0=2.54211e-014
请按任意键继续. . .

i=5时的5.68434e-014是怎么来的？？？

保留四位小数的输出方式

printf( "%.4lf", sqrt(r/n)); 

2019.3.3