1 #include<iostream>
 2 #include<string>
 3 #include<sstream>
 4 #include<set>
 5 
 6 using namespace std;
 7 
 8 int main()
 9 {
10     double sum=0.345666;
11     cout.precision(4);  //四舍五入，四位有效数字
12     cout<<sum<<endl;
13     return 0;
14 }