C++中小数点输出格式

#include<iostream>
#include<iomanip>
using namespace std;
int main(void){
    double s;
    cin>>s;
    
    if(s*95>=300){
        cout<<setiosflags(ios::fixed)<<setprecision(2)<<s*95*0.85<<endl;
    } 
    
    else{
        cout<<setiosflags(ios::fixed)<<setprecision(2)<<s*95<<endl;
    }
    
    
    return 0;
}

#include <iostream>
#include <iomanip>
using namespace std;

int main(void){
    double S = 0.000000123;
    double A = 456.7;
    double B = 8910000000000.0;

    cout << "default precision is "
         << cout.precision() << endl;    // 6

    cout << "    S = " << S << endl;    // 1.23e-07
    cout << "    A = " << A << endl;    // 456.7
    cout << "    B = " << B << endl;    // 8.91e+12

    cout << setiosflags(ios::showpoint)
         << "ios::showpoint ON" << endl;

    cout << "    S = " << S << endl;    // 1.23000e-07
    cout << "    A = " << A << endl;    // 456.700
    cout << "    B = " << B << endl;    // 8.91000e+12

    cout << resetiosflags(ios::showpoint)
         << "ios::showpoint OFF" << endl;
    cout << setiosflags(ios::fixed)
         << "ios::fixed ON" << endl;

    cout << "    S = " << S << endl;    // 0.000000
    cout << "    A = " << A << endl;    // 456.700000
    cout << "    B = " << B << endl;    // 8910000000000.000000

    cout << resetiosflags(ios::fixed)
         << setiosflags(ios::scientific)
         << "ios::scientific ON" << endl;

    cout << "    S = " << S << endl;    // 1.230000e-07
    cout << "    A = " << A << endl;    // 4.567000e+02
    cout << "    B = " << B << endl;    // 8.910000e+12
}