SMD Transistors

All the comments in this post  to you are completely valid and insightful.

Recommend you start with the basics - what is your logic voltage, what is the load (needing to drive) in mA or amps, and how fast does it need to switch ? If your logic is asynchronous, timing may not be critical, but if your logic is clocked, the transistor needs to be faster than the clock.    

All the comments in this post  to you are completely valid and insightful.

Recommend you start with the basics - what is your logic voltage, what is the load (needing to drive) in mA or amps, and how fast does it need to switch ? If your logic is asynchronous, timing may not be critical, but if your logic is clocked, the transistor needs to be faster than the clock.    

As I am a beginner in this field I don't know much but I am planning to make 8-bit adder with those transistors! after reading all the datasheet I decided to buy ss8050. Should this transistor work for this application?

posting schematics would be useful... SS8050 have maximum collector current of 1.5A - will they be used to drive some load? Or to implement some logic functions? Are you building this adder with only transistors or some ICs also?

Really hope you're going to simulate it before using up so many transistors! This isn't a beginners level project, expect to troubleshoot a lot unless you're really going to put effort into simulating, modular design, test features in your board, and so on. Also, at least test a single adder or two first. 

By the way there's a good chance of getting bad transistors if you're buying from unknown sources (I have no idea), and since you're a beginner, you might not know that,  therefore consider how you're going to either eliminate them, or how you will isolate faults and replace them (i.e. you'll need spares too..). 

Also, it's unlikely to perform like a modern digital circuit if you're solely constructing from NPN transistors. Again, lots of opportunities to trip up if you're a beginner.