QUESTION 41 · C fundamentals

State two practical rules for naming identifiers in C.

2 marks

Answer

Use a letter as the first character of a beginner-style name, followed by letters, digits or underscores; do not use a keyword.

total_marks is valid; 2marks and total-marks are not valid single identifiers.
Names are case-sensitive: total and Total are different. Avoid reserved underscore patterns.

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QUESTION 42 · C fundamentals

What are tokens and identifiers? Explain identifier naming rules in C.

5 marks

Answer in brief

Tokens are the small building blocks of C source code. An identifier is a name given to a variable, function or another program item.

Common token types

Keywords: Words with a fixed language meaning, such as int and while. They cannot be used as ordinary variable names.
Identifiers: Names selected by the programmer, such as total and calculate_sum.
Constants: Values written in the source, such as 25 or 3.5.
String literals: Text written in double quotes, such as "Hello".
Operators and punctuation: Symbols such as +, =, ; and braces help form expressions and statements. C calls these symbols punctuators.

Identifier naming rules

First character: For the simple portable names used here, begin with a letter.
Remaining characters: Use letters, digits and underscores. Spaces and hyphens cannot be part of one identifier.
Case matters: total and Total are different names.
Keywords are not allowed: Do not name a variable int or while.
Avoid reserved names: Do not use leading-underscore patterns in beginner application names.

Examples

total_marks and marks2 are valid names. 2marks is invalid because it begins with a digit. total-marks is read as subtraction, not one name. student count contains two separate names rather than one identifier.

Meaningful names

Choose names that explain the data, such as student_count or total_marks. The source int total = 25; contains the keyword int, identifier total, integer constant 25 and symbols = and ;. Do not memorise an old rule that all C names must have at most eight characters; implementations have limits, but useful names can be longer.

Reference tables

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Tokens in a declaration
Source fragment	Category	Meaning
int	Keyword	A built-in type specifier.
total	Identifier	A name chosen for the object.
=	Punctuator/operator	Assignment or initialisation notation in context.
25	Integer constant	A numeric value written in the source.
;	Punctuator	Ends the declaration.