how to print only one result from multiple regex (C++)

I'm trying to search with regex to find words like "long tonne" by ignoring any white spaces between "long" and "tonne", which I thought would be best with regex. with the code below, it will print out every converted output but I'm only trying to print one result. ex. if I enter 12 kg, I would only want my result to print the converted to lbs string.

So far, Ive tried :

• removing the semi colon after the regex
• adding { } brackets before if and after regex

• running the code section by section by copying and pasting in another project (which i feel its the regex that I'm having issues with)

  #include <iostream> 
  #include <string>
  #include <regex>
  using namespace std;
  int main() 
  { 
      cout << "Enter your mass with unit: "; 
      double earthMass;
      string unit; 
      string tolower(unit);
  
      cin >> earthMass >> unit;
  
      regex kg("kg|kgs");
      if (regex_match("kg", kg))
      {
          double dKgToLb;
          dKgToLb = (earthMass * 2.20462);
          cout << "your converted mass is : " << dKgToLb << " lb" << endl;
      }
      regex pound("lb|lbs");
      if (regex_match("lb", pound))
      {
          double dLbToKg;
          dLbToKg = (earthMass * 0.453592);
          cout << "your converted mass is : " << dLbToKg << " kg" << endl;
      }
      regex longTonne("long\\s*tonne|lg\\s*tn");
      if (regex_match("long tonne", longTonne))
      {
          double dLongToShort;
          dLongToShort = (earthMass * 1.12);
          cout << "your converted mass is : " << dLongToShort << " sh tn" << endl;
      }
      regex shortTonne("short\\s*tonne|sh\\s*tn");
      if (regex_match("short tonne", shortTonne))
      {
          double dShortToLong;
          dShortToLong = (earthMass * 0.892857);
          cout << "your converted mass is : " << dShortToLong << " lg tn" << endl;}
      }
      else if (!cin.good())
      {
          cerr << "your input is invalid\n";
          return EXIT_FAILURE;
      }
  }