Hi,
To create a new function open SCADA-Administrator -> Formulas table. It already contains a few examples.
If you need a formula to calculate input channel value, it should be as the following:
double MuFunc()
{
return 1; // for example
}
Then enter the formula in the Input channels table: MyFunc(); 1
Where 1 is status of the input channel.
Anyway the channel value is double. If you need string representation, use Unit table (find the example in the default configuration database).
Also read about using formulas at Part 3. Software Configuration in http://rapidscada.org/product/documentation/