You don't know the usage of stringstream

• Keep two decimal places and save to string
• stringstream and iostream The usage of is very similar

#include <sstream>
#include <iomanip>
#include <iostream>

using namespace std;

int main(int argc, char **argv) {
    
  double a = 0.13567;
  stringstream ss;
  ss << fixed << setprecision(2) << a;
  ss >> a;  // Save to double
  cout << ss.str() << endl;  //0.14

  return 0;
}

• Own implementation to retain two decimal places and save to the string
• Be careful ：+= Than + fast

string KeepTwo(double a) {
    
  int b = a * 100 + 0.5;
  string s;
  s += to_string(b/100) + ".";
  b %= 100;
  if( b  < 10) {
    
    s += "0";
  }
  s += to_string(b);

  return s;
}