When we create a variable, do we need to think about the size of the data type?
For example int myNum = 125; or byte myNum = 125;
I asked this question to know your ideas according to your practical experiences. Thanks!
Use int unless you have good reason to do otherwise. This is the "natural" size for the implementation.
long if values can reasonably be expected to exceed the range of plain integers.
short or byte if you're matching some external requirements (protocol structures, etc) or just possibly if you're expected a large (hundreds of thousands?) quantity of them.
As an example of the consideration I might give: let's say I need to generate an integer id for something. If I figure I might generate them once a millisecond on average, then using int I'm going to run out after about 27 days of uptime, which feels sort of low, so long seems a better choice.