THE # DEFINE DIRECTIVE in C Language

THE # DEFINE DIRECTIVE in C Language | Working of #Define

The #define directive is used to define a symbol to the preprocessor and assign it a value. The symbol is meaningful to the preprocessor only in the lines of code following the definition. For example, if the directive #define NULL 0 is included in the program, then in all lines following the definition, the symbol NULL is replaced by the symbol. If the symbol NULL is written in the program before the definition is encountered, however, it is not replaced.
The # define directive is followed by one or more spaces or tabs and the symbol to be defined. The syntax of a preprocessor symbol is the same as that for a C variable or function name. It cannot be a C keyword or a variable name used in the program; if it is so a syntax error is detected by the compiler.