A token in C can be defined as the smallest individual element of the C programming language that is meaningful to the compiler¹. It is the basic component of a C program.

The tokens of C language can be classified into six types based on the functions they are used to perform¹. The types of C tokens are as follows:

• Keywords: The keywords are pre-defined or reserved words in a programming language. Each keyword is meant to perform a specific function in a program. Since keywords are referred names for a compiler, they can’t be used as variable names because by doing so, we are trying to assign a new meaning to the keyword which is not allowed. You cannot redefine keywords. However, you can specify the text to be substituted for keywords before compilation by using C preprocessor directives. C language supports 32 keywords which are given below:

• Identifiers: Identifiers are used as the general terminology for the naming of variables, functions, and arrays. These are user-defined names consisting of an arbitrarily long sequence of letters and digits with either a letter or the underscore (_) as a first character. Identifier names must differ in spelling and case from any keywords. You cannot use keywords as identifiers; they are reserved for special use. Once declared, you can use the identifier in later program statements to refer to the associated value. A special identifier called a statement label can be used in goto statements¹.

• Constants: The constants refer to the variables with fixed values. They are like normal variables but with fixed values that cannot be changed during the program execution¹. Constants can be of any basic data type like an integer constant, a floating constant, a character constant, or a string literal². There are also enumeration constants as well.

• Strings: Strings are sequences of characters enclosed in double quotes (""). Strings are used to store text data and manipulate them using various string functions². Strings are treated as arrays of characters in C.

• Special Symbols: All characters except alphabets and digits are called special symbols². They are used to perform various operations in C programs. Some of the special symbols are: