title: How to swap two variable values?
body: <p>I'm writing a complex program that calculates change in potential energy( ΔPE= mgΔh ).</p>
  
  <pre><code>Console.WriteLine("Mass in kg");
  string cmMa = Console.ReadLine();
  double cMass;
  if(!Double.TryParse(cmMa, out cMass) )
  {
      Console.WriteLine("Only numbers!");
      Console.ReadLine();
  }
  Console.WriteLine("First height in m");
  string cfH = Console.ReadLine();
  double fH;
  if(!Double.TryParse(cfH, out fH))
  {
      Console.WriteLine("Only numbers!");
      Console.ReadLine();
  }
  Console.WriteLine("Second height in m");
  string csH = Console.ReadLine();
  double sH;
  if(!Double.TryParse(csH, out sH))
  {
      Console.WriteLine("Only numbers!");
      Console.ReadLine();
  }
  double ch = fH - sH;
  Console.WriteLine("Intermediate result: Change in height(Δh)= "+ch+" m" );
  Console.ReadLine();
  double ng = 9.81;  //   m/s^2
  Console.WriteLine("CHANGE IN POTENTIAL ENERGY: "+ch*cMass*ng+" J");
  </code></pre>
  
  <p>At the end, I want to add an if statement that if sH>fH, then their values are swapped. What concept should I apply? </p>