In the C programming language, which of the following identifiers cannot be used as a variable name (choose the reserved keyword that is invalid as an identifier)?

Introduction:
In C programming, identifiers (variable, function, and type names) must follow strict lexical rules. A common beginner trap is attempting to use a reserved keyword as a variable name. This question checks understanding of C's identifier syntax and the reserved keyword set.

Given Data / Assumptions:

• Language context: ANSI C / ISO C.
• Candidate names: else, coal, ram, vendy.
• Goal: identify the invalid variable name according to C rules.

Concept / Approach:

C identifiers must start with a letter or underscore and then may contain letters, digits, or underscores. However, no identifier may be a reserved keyword. Keywords have fixed meanings to the compiler and cannot be redefined as variable names. The token 'else' is a control-flow keyword paired with 'if' and 'else if' constructs, so it cannot be repurposed as an identifier.

Step-by-Step Solution:

Verification / Alternative check:

Compilers will emit a syntax error if you attempt int else = 5; because the parser expects the keyword 'else' to follow an 'if' statement, not to declare an object.

Why Other Options Are Wrong:

'coal' – not a keyword; valid identifier.
'ram' – not a keyword; valid identifier (despite being a common acronym).
'vendy' – not a keyword; valid identifier.

Common Pitfalls:

Confusing natural-language words with keywords; assuming case-insensitive matching (C is case-sensitive; 'Else' would be valid, though discouraged). Avoid shadowing and pick descriptive names even when valid.

Final Answer:

else