C tokens

Identifiers, keywords, datatypes, constant and variables.

1. C Programming Identifiers, Keywords, Datatypes, Constants and Variables

2. Identifiers In C programming, identifiers are name given to C entities, such as variables, functions, structures etc. An identifier can be composed of letters such as uppercase, lowercase letters, underscore, digits, but the starting letter should be either an alphabet or an underscore. Keywords cannot be represented as an identifier. The length of the identifiers should not be more than 31 characters. Identifiers should be written in such a way that it is meaningful, short, and easy to read. For example: Total, sum_1, average, _money

3. Keywords Keywords are the words whose meaning has already been explained to the C compiler. We cannot use it as a variable name, constant name, etc.  We can also call as reserved words in C. There are only 32 reserved words (keywords) in the C language. auto break case char const continue default do double else enum extern float for goto if int long register return short signed sizeof static struct switch typedef union unsigned void volatile while

4. Data Types A data type specifies the type of data/value we want to store in a variable.

5. Data type and Sizes Type name 32-bit size Format specifier Range char 1 byte %c (-128 to 127) or (0 to 255) int 2 or 4 bytes %d -32768 to 32767 or -2147483648 to -2147483647 float 4 bytes %f 1.2E-38 to 3.4E+38 double 8 bytes % lf 1.7E-308 to 1.7E+308 Each data type requires different amount of memory. Different data types also have different ranges up to which they can store numbers. These ranges may vary from compiler to compiler.

6. Constants Constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. 

7. Constants If we want to define a variable whose value cannot be changed, we can use the const keyword. const double PI=3.14; We can also define a constant using #define preprocessor directive. #define PI 3.14

8. Variables A  variable  is a name of the memory location. It is used to store data. Its value can be changed, and it can be reused many times. It is a way to represent memory location through symbol so that it can be easily identified. Syntax to declare variable Data type variable_name Example: int a; char b; float c; Here, a, b, c are variables. The int, char, float are the data types. We can also provide values while declaring the variables int a=10; char b='A';   float c=20.8;  

9. Rules for variable name A variable can have alphabets, digits, and underscore. A variable name can start with the alphabet, and underscore only. It can't start with a digit and blank spaces. No whitespace is allowed within the variable name. A variable name must not be any reserved word or keyword, e.g., int, float, etc.

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