設置C++ cout輸出精度

cout.precision(5);
數字表示小數點位數

// modify precision
#include <iostream>     // std::cout, std::ios

int main () {
  double f = 3.14159;
  std::cout.unsetf ( std::ios::floatfield );                // floatfield not set
  std::cout.precision(5);
  std::cout << f << '\n';
  std::cout.precision(10);
  std::cout << f << '\n';
  std::cout.setf( std::ios::fixed, std:: ios::floatfield ); // floatfield set to fixed
  std::cout << f << '\n';
  return 0;
}