Hi, I am developing a project that is based on the serial communication of arduino with an interface in labview, the detail is that I can not convert the data (decimal number) into an analogue number, since I need to vary the amplitude of an electrical resistance for water heating, I would appreciate your help
You've used two words in a funny way so I'm not sure you mean what they really mean.
Can you define these two words, what they mean to YOU in your own words?
decimal number
analogue number
What you say now doesn't make sense. There's no such thing as an "analogue number" and decimal number just means that the number is written in base 10.
I need to vary the amplitude of an electrical resistance for water heating,
How are you going to do that? The Arduino is not a programmable potentiometer.
You can use the Arduino with a digital potentiometer such as these digital potentiometer - Google Search. This will be fine for controlling a circuit but...
... they are not for carrying any significant current/voltage. So if you want to control the power to a heating element you will have to have something rather more robust. Google will help with lots of options you can build or buy depending upon your requirements.