C++ Programming Code Examples
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#ifndef Directive in C++ Programming Language
#ifndef Directive in C++
The #ifndef directive of the C++ Programming Language helps in allowing the conditional compilation. The C++ Programming Language's preprocessor helps in determining only if the macro provided is not at all existed before including the specific subsequent code in the C++ compilation process. The #ifndef preprocessor only checks If the specific macro is not at all defined with the help of the #define directive. If the condition is TRUE then it will be helpful in executing the code otherwise the else code of the #ifndef will be compiled or executed only if present.
Syntax for #ifndef Directive in C++
#ifndef MACRO
//Code Statements
#else
//Code Statements which are used to include if the specific token is defined
#endif
#ifndef MACRO
The #ifndef works for the opposite condition of the #ifdef directive of the C Programming Language. The "MACRO" definition should not be defined for the specific preprocessor which is used to include the C Programming Source Code into the specific compiled application. The #ifndef must be ended with the #endif directive of the C Programming Language.
#else directive
If the #ifndef does not accept then else code statements will be printed which are actually used in including the specific which is defined.
#endif directive
The #endif directive of the C Programming Language helps in closing the #ifndef directive of the C Programming Language. It is must and should end only with the #endif C Source code directive.
The $ifndef directive usually checks/helps in seeing the specific identifier is currently not defined or not. The #ifndef preprocessor of the C Programming Language helps in allowing the conditional compilations. The preprocessor directive helps in determining whether the macro is existed or not before the subsequent code in the compilation process/ procedure.
The #ifndef directive and #if !defined identifier are equivalent directives of the C Programming Language. The #ifndef directive helps in checking the opposite condition of the #ifdef directive of the C Programming Language. If the specified identifier is not even defined or definition is removed with the help of the #undef then the condition is TRUE for nonzero value or else the condition will be FALSE.
/* #ifndef Directive in C++ language */
#define Module101
#define MyVersion 1.1
#include<iostream>
usingnamespace std;
int main(void)
{
cout<<"Sample using #define, #ifdef, #ifndef"<<endl;
cout<<" #undef, #else and #endif..."<<endl;
cout<<"-------------------------------------"<<endl;
#ifdef Module102
cout<<"\nModule102 is defined."<<endl;
#else
cout<<"\nModule102 is not defined."<<endl;
#endif
#ifndef MyVersion
cout<<"\nMyVersion is not defined"<<endl;
#else
cout<<"\nMyVersion is "<<MyVersion<<endl;
#endif
#ifdef MyRevision
cout<<"\nMy Revision is defined\n"<<endl;
#else
cout<<"\nMyRevision is not defined!"<<endl<<endl;
#endif
#undef MyVersion
#ifndef MyVersion
cout<<"MyVersion is not defined"<<endl<<endl;
#else
cout<<"MyVersion is "<<MyVersion<<endl;
#endif
return 0;
}
To convert "Hexadecimal" number to "binary" number in C++, you have to ask to the user to enter the hexadecimal number to convert it into binary number to display the equivalent
