#include <iostream.h>

// file: tfuncts.cc
// Functions that return values
// convert between Celsius and Fahrenheit (revised)

double FtoC(double tempFahr)
{
   return (tempFahr+40.0)*5.0/9.0 - 40.0;
}

double CtoF(double tempCels)
{
   return (tempCels+40.0)*9.0/5.0 - 40.0;
}

int main()
{
   double Cels, Fahr;

   cout << "Enter a Fahrenheit temperature: ";
   cin >> Fahr;
   cout << "That converts to " << FtoC(Fahr) << " Celsius." << endl;

   cout << "Enter a Celsius temperature: ";
   cin >> Cels;
   cout << "That converts to " << CtoF(Cels) << " Fahrenheit." << endl;

   return 0;
}

Sample output:

< tfuncts
><Enter a Fahrenheit temperature: 100
< That converts to 37.7778 Celsius.
><Enter a Celsius temperature: 100
< That converts to 212 Fahrenheit.

< tfuncts
><Enter a Fahrenheit temperature: 68
< That converts to 20 Celsius.
><Enter a Celsius temperature: -40
< That converts to -40 Fahrenheit.