Use of the Directive

[rachelle]

What is the use of #if directives in C programming language. If someone could provide me the syntax and it would help me a lot.

[Ralph]

The #if directive controls compilation of portions of a source file. If the expression you write after the #if have a nonzero value, the line group immediately following the #if directive is retained in the translation unit.

[Sandhya.Kishannag]

The syntax of #if is #if constant-expression newline

This directive checks whether the constant-expression is true (nonzero). The operand must be a constant integer expression that does not contain any increment (++), decrement (- -), sizeof , pointer (*), address (&), and cast operators. The constant expression in an #if directive is subject to text replacement and can contain references to identifiers defined in previous #define directives. The replacement occurs before the expression is evaluated.