ExplanationThe execution of the above program is same as the previous one. The only difference is
in the name of the identifier. Here, in this program the identifier is E. The compiler searches for the
identifier E. If it is found then execution of #i f block takes place otherwise #else block. The #end± f
statement indicates the end of # i f #endi f block.
11.7 THE #ifndef DIRECTIVE
The syntax of the #if ndef directive is given below.
Syntax
#ifndef <identifier>
{
statement!;
statement2;
}
#else
{
statement3;
statements
}
#endif
The#ifndef works exactly opposite to that of #ifde
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