C identifier rules: Which special symbol is allowed within a variable name according to standard C/C++ naming conventions?

Introduction / Context:Valid identifiers are essential for readable, portable code. C and C++ restrict variable names to a specific character set so compilers can parse tokens unambiguously. This question checks your knowledge of which special symbol is permitted within a variable name without invoking operator parsing or undefined behavior.

Given Data / Assumptions:

• Identifiers typically consist of letters (A–Z, a–z), digits (0–9), and possibly one special character.
• The first character of an identifier cannot be a digit.
• We are concerned with ASCII-like basic source character set; extended identifiers exist but are not the focus.

Concept / Approach:

• The only commonly allowed special character in standard C/C++ identifiers is the underscore ''.
• Other symbols like '', '|', and '-' are operators or punctuation and cannot appear in identifiers.
• Although identifiers beginning with underscores may be reserved in certain contexts, underscore itself is permitted.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• *, |, -: These are operators with fixed meanings in expressions and cannot appear in identifiers.
• None of the above: Incorrect because underscore is valid.

Common Pitfalls:

• Using identifiers beginning with an underscore plus a capital letter or double underscore; these are reserved for the implementation.
• Starting identifiers with digits; that is invalid syntax.

Final Answer: