Identifier

An identifier is a sequence of letters and digits. Identifiers are created to give unique name to C entities to identify it during the execution of program. It means names given to various program elements, such as variables, function, etc..,

Rules for naming an Identifier

1. The first character must be “_”( underscore ) or any alphabet character.
   Ex: abc_, a_bc, a1bc, A1_bc
2. We can use both upper and lower case but upper case character is not equal to lower case character.
   Ex: abc is not equal to ABC
3. Keyword, special symbols and space are not allowed.
   EX: int, void, $abc, 1abc, a bc
4. An identifier can be of any length while most of the C compiler recognizes only the first 31 characters.

The following program will helps you to understand more about Identifier.

// Identifiers are in this program : MD_SN, abc, ABC, a_bc1, A_BC2
#include <stdio.h>
  int MD_SN();
  char abc='M', ABC='D', a_bc1='S', A_BC2='N';
  int main()
  {
  MD_SN();
  return 0;
  }
  int MD_SN()
  {
  printf("%c%c%c%c",abc,ABC,a_bc1,A_BC2);
}

Output

MDSN

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