1.7 — Keywords and naming identifiers

https://www.learncpp.com/cpp-tutorial/keywords-and-naming-identifiers/

1. How many keywords are reserved in C++ as of C++23?

92

2. Why can't you use C++ keywords as variable names?

Because they are reserved and have special meaning in the language

3. Which of the following is NOT a valid identifier in C++?
   a) myVariable
   b) myVariable c) 2myVariable d) myvariable

c) 2myVariable

4. What does C++ require as the first character of an identifier?

A letter (uppercase or lowercase) or an underscore

5. Which naming convention is unconventional for variable names in C++?
   a) int value;
   b) int Value;
   c) int myVariableName;
   d) int myvariablename;

b) int Value;

6. What is a disadvantage of using names like int _count; in your programs?

Identifiers starting with an underscore are typically reserved for OS, library, or compiler use

7. What does the following variable name likely fail to clarify? int time;

It doesn’t specify the unit (e.g., seconds, minutes, hours)

8. Which of these is a well-named identifier?
   a) int data;
   b) int x1;
   c) int numApples;
   d) int i;

c) int numApples;

9. What does the term “camelCase” refer to in identifier naming?

A convention where multi-word names start with a lowercase letter and each subsequent word starts with an uppercase letter (e.g., myVariableName)

10. What is the key insight mentioned regarding writing vs. reading code?

Code is read more often than it is written, so writing readable code saves time in the long run

Is this conventional, unconventional, or invalid? - int sum {};

Conventional

Is this conventional, unconventional, or invalid? - int _apples {};

Unconventional -- variable names should not start with an underscore.

Is this conventional, unconventional, or invalid? - int VALUE {};

Unconventional -- single word names should be in all lower case.

Is this conventional, unconventional, or invalid? - int my variable name {};

Invalid -- variable names can not contain spaces.

Is this conventional, unconventional, or invalid? - int TotalCustomers {};

Unconventional -- variable names should start with a lower case letter.

Is this conventional, unconventional, or invalid? - int void {};

Invalid -- void is a keyword.

Is this conventional, unconventional, or invalid? - int numFruit {};

Conventional

Is this conventional, unconventional, or invalid? - int 3some {};

Invalid -- variable names can not start with a number.

Is this conventional, unconventional, or invalid? - int meters_of_pipe {};

Conventional

C++ special identifies

override, final, import, and module

• Name of variable is called

An identifier

Rule 1 of identifier naming

• The identifier can not be a keyword. Keywords are reserved.

Rule 2 of identifier naming

• The identifier can only be composed of letters (lower or upper case), numbers, and the underscore character.

• That means the name can not contain symbols (except the underscore) nor whitespace (spaces or tabs).

Rule 3 of identifier naming

• The identifier must begin with a letter (lower or upper case) or an underscore. It can not start with a number.

Rule 4 of identifier naming

• C++ is case sensitive, and thus distinguishes between lower and upper case letters. nvalue is different than nValue is different than NVALUE.

It is conventional in C++ that variable names should begin with?

a lowercase letter.

If the variable name is a single word or acronym?

• the whole thing should be written in lowercase letters.

Identifier names that start with a capital letter are typically used for

• user-defined types

If the variable or function name is multi-word, there are two common conventions:

Either use underscores as spaces, or capitalize each word to separate them

When working in an existing program…

use the conventions of that program (even if they don’t conform to modern best practices)

Use modern best practices when…

• you’re writing new programs.

Avoid naming your identifiers starting with an…

underscore. That’s typically reserved for OS, library, and/or compiler use.

The name of your identifiers should

make clear what the value they are holding means

int ccount

Bad

What does the c before “count” stand for?

int customerCount

Good

Clear what we’re counting

int i

Either

Okay if use is trivial, bad otherwise

int index

Either

Okay if obvious what we’re indexing

int totalScore

Either

Okay if there’s only one thing being scored, otherwise too ambiguous

int _count

Bad

Do not start names with underscore

int count

Either

Okay if obvious what we’re counting

int data

Bad

What kind of data?

int minutesElapsed

Either

Okay if obvious what this is elapsed from

int x1, x2

Either

Okay if use is trivial, bad otherwise

int userinput1, userinput2

Bad

Hard to differentiate between the two due to long name

int numApples

Good

Descriptive

int monstersKilled

Good

Descriptive

Code is read more often than it is written, so…

any time saved while writing the code is time that every reader, including future you, will waste while reading it

For variable declarations, it can be useful to use…

• a comment to describe what a variable is going to be used for, or to explain anything else that might not be obvious.

An identifier that exists for only a few statements (e.g. in the body of a short function)

• can have a shorter name.

An identifier that is accessible from anywhere

might benefit from a longer name.

An identifier that represents a non-specific number (e.g. anything the user provides)

• can have a shorter name.

An identifier that represents a specific value (e.g. the length of an inseam in millimeters)

should have a longer name.