Is this the correct approach to do input validation with floating point values?

Question

After spending a good amount of time researching input validation, I combined a few ideas and came up with this:

Function to check a string for a valid dou

Answer 1

If it's an exercise you want, that's understandable. But otherwise, you can use istringstream to avoid reinventing the wheel:

#include 
#include 
#include 

using namespace std;

int main () {

  int n,val;
  string stringvalues;

  stringvalues = "3.14159254 f01fhasfljk";
  istringstream iss(stringvalues);

  float x,y;
  iss >> x;

  cout << x * 2 << endl;

  iss >> y;
  if ( ! iss.fail() )
    {
      cout << y * 2 << endl;
    }
  else
    {
      cout << "second value not a number..." << endl;
    }

  return 0;
}