What is identifier in C?

• Keywords are pre-defined words in a C compiler. Each keyword is meant to perform a specific function in a C program.
• Since keywords are referred names for compiler, they can’t be used as variable name.

• Below are some of keywords that C language offers.
• auto, double, int, struct, break, else, long, switch, case, enum, register, typedef, char, extern, return, union, const, float, short, unsigned, continue, for, signed, void, default, goto, sizeof, volatile, do, , if, static, while

• Constants refer to fixed values. They are also called as literals.
• C Constants are also like normal variables. But, only difference is, constant values can’t be modified by the program once they are defined. Constants may be belonging to any of the data type.

• Integer constants
• Real or Floating point constants
• Octal & Hexadecimal constants
• Character constants
• String constants
• Backslash character constants

• C variable is a named location in a memory where a program can manipulate the data. This location is used to hold the value of the variable.
• The value of the C variable may get change in the program.
• C variable might be belonging to any of the data type like int, float, char etc.

Constant values can’t be modified by the program once it is declared. But, variable values can be modified by the program.

No. Variable names can’t start with numbers as per the variable naming rule.

• Variable declaration tells the compiler about data type and size of the variable. Whereas, variable definition allocates memory to the variable
• Variable can be declared many times in a program. But, definition can happen only one time for a variable in a program.
• Variable declaration is for assignment of properties and identification to a variable. Whereas, variable definition is for assignments of storage space to a variable

• Local variable
• Global variable
• Environment variable

• The variables which are having scope/life only within the function are called local variables.
• These variables are declared within the function and can’t be accessed outside the function.