2023.8.11 周五：保留小数点后几位

#include <iostream>
#include <iomanip>
int main()
{
    int n;
    cin >> n;
    double PI = 3.14159265358979;
    cout << setprecision(n) << fixed << PI << endl;
    return 0;
}

#include <stdio.h>
int main()
{
    double PI = 3.14159265358979;
    printf("%.4f\n",PI);
    return 0;
}

//java
System.out.println(String.format("%.2f",num));