Question

Identify invalid variable names from the following, give reason for each:
Group, if, int, total marks, S.I., volume,
tot_strength, 9t, tag$

Answer 1

Answer:

Variable names in C are made up of letters (upper and lower case) and digits. The underscore character ("_") is also permitted. Names must not begin with a digit. Unlike some languages (such as and some dialects), C does not use any special prefix characters on variable names.

Some examples of valid (but not very descriptive) C variable names:

foo

Bar

BAZ

foo_bar

_foo42

_

QuUx

Some examples of invalid C variable names:

2foo (must not begin with a digit)

my foo (spaces not allowed in names)

$foo ($ not allowed -- only letters, and _)

while (language keywords cannot be used as names)

As the last example suggests, certain words are reserved as keywords in the language, and these cannot be used as variable names.

It is not allowed to use the same name for multiple variables in the same . When working with other developers, you should therefore take steps to avoid using the same name for global variables or function names. Some large projects adhere to naming guidelines

to avoid duplicate names and for consistency.

In addition there are certain sets of names that, while not language keywords, are reserved for one reason or another. For example, a C compiler might use certain names "behind the scenes", and this might cause problems for a program that attempts to use them. Also, some names are reserved for possible future use in the C standard library. The rules for determining exactly what names are reserved (and in what contexts they are reserved) are too complicated to describe here

[]

, and as a beginner you don't need to worry about them much anyway. For now, just avoid using names that begin with an underscore character.

The naming rules for C variables also apply to naming other language constructs such as function names, struct tags, and macros, all of which will be covered later.