What is enum in C?

• Void is an empty data type that has no value.
• We use void data type in functions when we don’t want to return any value to the calling function.
• Example:

void sum (int a, int b); – This function won’t return any value to the calling function.
int sum (int a, int b); – This function will return value to the calling function.

• We use void data type in pointer like “void *p”. It means, pointer “p” is neither pointing to int data type nor char data type. It acts as generic pointer. We are using void pointer when we are not sure on the data type that this pointer will point to. We can use void pointer to refer either integer data or char data. But, this void pointer should not be dereferenced without explicit type casting.
• We use void in functions as “int function_name (void)”. Here void means, this function does not pass any argument.

• C tokens are the basic buildings blocks in C language which are constructed together to write a C program.
• Each and every smallest individual unit in a C program are known as C tokens.

• C tokens are of six types. They are,

  1. Keywords               (eg: int, while),
  2. Identifiers               (eg: main, total),
  3. Constants              (eg: 10, 20),
  4. Strings                    (eg: “total”, “hello”),
  5. Special symbols    (eg: (), {}),
  6. Operators              (eg: +, /,-,*)

• Each program elements in a C program are given a name called identifiers.
• Names given to identify Variables, functions and arrays are examples for identifiers.
• Example: x is a name given to integer variable in above program

• 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.