C++ Help

[Cruise Control]

I need help, how in blaspheme do I pass data? Can I get an example

  float c(float fa, float ce);
  float f(float fa, float ce);

 int main()
  {
   float choice; //Stored for intial choice.

   cout << "This will convert fahrenheit to celsius.";
   cout << "What do you want to start with, enter your number than print enter.\n";
   cout << " 1. Fahrenheit\n";
   cout << " 2. Celsius\n";
   cin >> choice;

   if (choice==1)
    f();
   else
    c();
 return 0;
}

float c(float fa, float ce)
{
 float fa; //Fahrenheit variable.
 float ce; //Celsius variable.

 cout << "Input your fahrenheit vaulue and press\nENTER.\n";
 cin >> ce;
 fa=1.8*ce+32;
}

float f(float fa, float ce)
{
 float fa; //Fahrenheit variable.
 float ce; //Celsius variable.
 cout << "Input your celsius vaulue and press\nENTER.\n";
 cin >> fa;
 ce=(fa-32)/1.8;

}