What is valid and invalid c variable names?

Excerpt§

This post covers the specific rules and conventions for valid and invalid variable names in C programming. Learn what makes a variable name legal or illegal.

When writing code in the C programming language, one of the first things you have to do is name your variables. The names you choose for your variables can have a big impact on the readability and maintainability of your code. In C, there are specific rules and conventions for what makes a valid variable name versus an invalid one. This blog post will cover the dos and don’ts of C variable naming.

Introduction to C Variable Naming Conventions§

In C, all variable names must adhere to certain syntax rules in order to be valid. Some key points:

• Variable names can contain letters, numbers, and underscores.
• The first character of a variable name must be a letter or underscore.
• C is case-sensitive - myVar and myvar are different variables.
• Variable names cannot contain spaces or special characters like &, *, $, etc.
• Names cannot conflict with C keywords like if, else, int, etc.

Following these rules allows C to easily distinguish variable names from other tokens in your code. Trying to use an invalid name will result in a compiler error.

Rules for Valid Variable Names§

Here are the specific requirements for a legally valid variable name in C:

• The name can begin with a letter (A to Z or a to z) or an underscore (_).
• After the first character, the name can also contain digits (0 to 9).
• C variable names are case-sensitive, so myVar and myvar are different names.
• The length of the variable name can be up to 31 characters.
• You cannot use C reserved keywords like int, char, if, etc. as variable names.

Some examples of valid variable names:

1int pageCount;
2char firstLetter;
3double account_balance;
c

As long as you follow these rules, the C compiler will accept your variable names.

Below I will provide you with several free online variable conversion tools:

Common Rules for Invalid Names§

There are some clear rules that will make your variable name invalid in C:

• The name cannot begin with a digit (0-9). It must start with a letter or underscore.

• You cannot have spaces or special characters like &, *, $ in the name.

• Avoid very short names like x or q that don’t indicate the meaning.

• Don’t use extremely long names of more than 31 characters.

• Avoid plural names like customers - it’s better to use customer for a single variable.

Some examples of invalid variable names:

1int 1value; // Starts with number
2int full name; // Contains space
3int *ptr; // Contains special character
c

Trying to use these kinds of names will result in compiler errors.

Examples of Valid and Invalid Names§

To solidify your knowledge, here are a few more examples of valid and invalid C variable names:

Valid:

1int wheelsOnBus;
2char firstLetter;
3float account_balance_usd;
c

Invalid:

1int bus#; // Special character
2float full name; // Space in name
3int else; // C keyword
4int veryVeryLongNameOver31Chars; // Over 31 characters
c

Take note of the exact reasons that make each invalid name illegal in C.

Why Variable Naming Rules Matter§

You may be wondering why C enforces these seemingly arbitrary rules for variable names. There are good reasons:

• The rules help avoid name conflicts with language keywords and built-in identifiers.
• Consistent naming conventions improve the readability of code.
• Names like index and customerName are more self-documenting than short ones like i and cN.
• Invalid names like spaces and special characters can cause major errors.

Adhering to C’s rules for variable naming will make your code cleaner and less error-prone. While simple programs may work even with sloppy naming, it’s best practice to follow the standard conventions.

Summary of Key Points§

To recap the key points on C variable naming:

• Variable names begin with a letter or underscore, and can contain letters, numbers, and underscores.
• Names are case-sensitive and can be up to 31 characters long.
• Invalid names include those starting with a number, containing spaces/special characters, or conflicting with keywords.
• Following the standard naming conventions avoids errors and improves readability.
• Choosing descriptive names like customerCount makes your code easier to follow.

Be sure to avoid the common mistakes that can arise from something as simple as a variable name. Though the compiler will catch invalid names, following best practices from the start will save you headaches down the road!