You want to convey information quickly. Consider using Hungarian Notation. Hungarian notation uses lower case characters that indicate the type of a variable as the name's prefix. Then, you can look at any variable and instantly know it's type, crucial in a language like C that lets you get away with murder in parameter passing and creating expressions. Form the rest of the name by capitalizing the first letter of each word.
Success lies in defining a set of standard types and the abbreviation for each.
Note that Hungarian even supports structures and other complex types. Underscores are not really needed with Hungarian Notation. Global Variables Don't use globals. Tears come to my eyes looking at the average embedded program, which is invariably riddled with hundreds or thousands of globals. Every little function seems to access this vast hoard of data, changing a bit here or complementing a word there.