Should I initialize variables separately from declaring them?

Question

I am learning C language. In the book, it says:

"initialize a variable when declaring it only if the initial value is part of the semantic of the variable. If the initial value is part of an algorithm, use a separate assignment statement. For example, instead of

int price = units * UNIT_PRICE;
int gst = price * GST;

Write

int price, gst;

 price = units * UNIT_PRICE;
 gst = price * GST;

I do not understand why we should do that? What are the reasons behind it?

Answer 1

This is really just a matter of programming style. What the author is probably saying is that separating the declaration from a normal assignment makes the code cleaner and easier to understand at a glance. If, on the otherhand, the initial assignment is part of the meaning of the variable, then it's ok to combine declaration and definition. An example of this might be an int with a boolean value such as int AnExceptionHasOccurred = FALSE.

Answer 2

So long as you absolutely set a value before you use it, it doesn't matter how you do it. It's generally good style to set some reasonable default or sentinel value initially though, if it may change later.

This is because you have no guarantees what an uninitialized variable may have for a value if referenced before set, and it's a style bug.