model goo

  parameter Real x;

  constant Integer c = 3;

  Real y



equation

  y = c * x;

end goo;

y is a variable that will be calulated in the simulation, x is a variable that you can change before a simulation (but will held cosntant from t=0 until t=end) and c is a constant that you define in the model and can not be change directly.

hope it helps.One good read about modeling in modelica could be found in http://book.xogeny.com/ if you are interested.

cheers

Hello,
  thank you @Arinomo23, your answer it was helpful
now I have another question if you want, it is about blocks in OpenModelica, so can you tell me how I can create a block MIMO in OpenModelica and how I can specify the inputs and the outputs in the programme that I will write in this block,
thank you in advance for your answer.
 

Abderezakabidi,
  hello,

    I want to create two blocks in OpenModelica and to connect between them, such that the second block's inputs are the first block's outputs.
can you help me to do this, please?
thank you