Technology & IT Skills

Using Keywords for Variable Names in C: Naming Rules Quiz

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This quiz helps you check variable naming in C and avoid using keywords for variable names, so your identifiers compile cleanly. You will get instant feedback on what names are allowed and which reserved words as identifiers will break a build. After this, sharpen more skills with our C programming quiz, explore challenges to practice c code online, or time yourself with a fast c coding test.

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1Which of these variable names is invalid because it begins with a digit?
2Which of the following is not a valid C variable name because it is a reserved keyword?
3According to the C standard, identifiers beginning with two underscores are reserved for the implementation in all contexts. Which of the following names falls into this reserved category?
4Which of the following characters is valid as the first character of a C variable name?
5Which of these names should be avoided because it is reserved by the C standard for the implementation (compiler or standard library)?
6Which of the following is not a valid C variable name because it contains an invalid character?
7Which of the following is a valid C variable name?
8Which of the following best describes the valid starting characters for a C variable name?
9Which of the following statements about identifiers starting with an underscore is correct according to the ISO C standard?
10Which identifier starting pattern is reserved by the C standard in all contexts?
11Which of the following characters cannot start a C variable name but is used to denote preprocessor directives?
12What does the notation "\\uXXXX" in an identifier represent in C11, and under what condition can it serve as the first character?
13Identifiers starting with an underscore and a lowercase letter are reserved for which scope according to the C standard?
14Which of the following identifier starting patterns is NOT reserved by the C standard in any context?
Learning Goals

Study Outcomes

  1. Understand C variable naming rules -

    Describe the fundamental constraints of C identifiers, including why a C variable cannot start with a digit or special symbol.

  2. Identify invalid starting characters -

    Spot when a C variable begins with prohibited characters like numbers or symbols, preventing compilation errors.

  3. Analyze common naming pitfalls -

    Differentiate between valid and invalid variable names, recognizing issues such as reserved keywords or unconventional formats.

  4. Apply correct naming conventions -

    Construct clear, consistent identifiers that comply with C's rules and enhance code readability.

  5. Evaluate and correct variable names -

    Review sample code to detect naming violations and refactor identifiers for error-free compilation.

Study Guide

Cheat Sheet

  1. Valid Identifier Start Characters -

    According to ISO/IEC 9899:2018, a C variable must begin with a letter (A - Z or a - z) or an underscore (_), ensuring consistency across compilers (see C11 standard). For example, _count and data1 are valid starts, whereas 1data is not. Remember the rule: "start smart, choose letters or underscores."

  2. Digits and Special Symbols Are Off-Limits -

    In C, a C variable cannot start with a digit or symbol like $, %, or @, even if some compilers allow extensions (per university tutorials such as those at MIT OCW). Writing 9lives or $price will trigger a compile-time error. Keep in mind: "no numbers or special chars at the very beginning."

  3. Reserved Keywords and Namespaces -

    You can't use reserved words (e.g., int, return) as identifiers, as defined by K&R and the official ANSI C standard. Also, avoid leading underscores followed by uppercase letters or double underscores, since these are reserved for the implementation (GNU C manual). Choose names like myValue instead of __MyValue.

  4. Case Sensitivity and Naming Conventions -

    C is case-sensitive, so Value and value are distinct variables (per Stanford CS Education Library). While uppercase starts are allowed, many style guides (e.g., Linux kernel) recommend lowercase and snake_case for readability, like total_count. Consistency builds confidence and prevents subtle bugs.

  5. Mnemonic Tricks for Quick Recall -

    Use memory aids like "LUCK" - Letter or Underscore, Cannot start with a digit, Keywords forbidden - and remember "c variable cannot start with" anything else. This simple phrase helps cement naming rules from educational sites like GeeksforGeeks. A catchy mnemonic turns rules into reflexes!

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Updated Feb 18, 2026