there are some conventions in C++ language in naming the variables, objects, functions, etc... . And for example the convention for naming classes are: the 1st letter should be UPPERCASE and there shouldn't be any "_"-underscore character to divide letters but there should be each new word written with UPPERCASE letter: For example: "SimpleClass" or "MyNewClass".
Or one example for writing functions: "simpleFunction()", "myFunction()".
AND THE QUESTION IS:
Why for example the class from <string> library is written as "string" (or "basic_string<char>") or some variables are written as "out_of_scope". So that they are written WITH UNDERSCORE and classes WITH SMALL LETTERS?