#define: why uppercase?

Question

When defining a macro (e.g. #define BALL). Why do people use uppercase letters? I can write something like #define ball. It is not in uppercase, but it works.

Answer 1

It's convention. It makes reading and understanding code easier. It's not required, but recommended.

Answer 2

Why do you use _ for long variable names ? And why don't you just name variables as a or b because It is easy to understand and debug.

Using a variable name such as TotalHeight makes more sense than simple i. Some people even prefix the data type such as Int_TotalHeight. Its easy to maintain the code.

To answer your question, people use it for more understanding. Usually

1)To differentiate the variable name and macro name

 #define MAX 45 // easy to understand, it is a macro
 int max=45;

2)To differentiate the function from a macro. Say

 #define MULT(x, y) (x) * (y) 
 int mult(int,int);