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C Keywords & Identifiers

The C Character Set

In C programming, the character set consists of alphabets (Uppercase & Lowercase), digits & some special characters.


Uppercase : A, B, C, D, E, ……. , X, Y, Z.

Lowercase : a, b, c, d, e, …….. , x, y, z.


0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Special CharactersSpecial Characters Table

Whitespace Characters

Whitespace Characters include blank space, form feed, horizontal tab, new line & vertical tab.

C Keywords

C keywords are also known as reserved words.

They have unique and fix meaning.

They must be used at certain places only.

They are used to decide the type of identifiers

There are 32 keywords available in C.

They are always in lowercase.

C Keywords

For example

C Programming Keyword & Identifier Example

Here keyword decides the type of identifier as int.

Therefore identifier stores only int (integer) type value.

If we try to assign the value of another type to number identifier, C program will show error.

C identifiers

These are the words/names defined by the user for the entities like arrays, functions, structure, variable, etc.

For example

int salary;

float percentage;

It is better to define meaningful identifiers so that it becomes easy to recognize there meaning and work.

Rules for defining an identifier

Identifiers should consist of alphabets, digits and underscore sign (no other special characters are allowed).

It must always start with an alphabet or underscore.

Alphabets can be both uppercase and lowercase.

It must not be any keyword.

Generally, most of the compilers support a combination of 1 to 31 characters for defining identifiers.

Some compiler allows identifiers with more than 31 characters.

Blank spaces are not allowed within the identifier.

Commas are not allowed within identifiers.


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