Preprocessor Directive :


Preprocessor commands are called DIRECTIVES, and begin with a pound / hash symbol(#).

Example :

  1. /* Description: Area of circle use define in C++ language */
  2. #include<iostream>
  3. #define PI 3.14159
  4. using namespace std;
  5. int main()
  6. {
  7. int r=10;
  8. float cir;
  9. cir=PI*(r*r);
  10. cout<< "Area of circle: " <<cir <<endl;
  11. }

Output :

C++ language Area of circle use define

Note : No white space should appear before the #, and a semi colon is NOT required at the end. The #define preprocessor allows us to define symbolic names and constants :

#define PI

This statement will translate every occurrence of PI in the program (Example: #define PI 3.14159 ).

#define MAX

Before compilation, if the C++ preprocessor finds the MAX as one word, in the source code, it replace the number (Example: #define MAX 70 ).

#define NAME

Every time the preprocessor sees NAME it will replace it(Example : #define NAME"Computer Science C++"). This feature is particularly use for defining 'magic' numbers. An advanced use of #define is in the creation of macros.

Structure with #define :

Some time Create a big structure program using #define is helping much so, lets make a simple structure program using #define MAX in C++ language.

Example :

  1. /* Description: simple structure program using define MAX in C++ language */
  2. #include<iostream>
  3. #define MAX 2
  4. using namespace std;
  5. struct data{
  6. char name[20];
  7. }info[4];
  8. int main()
  9. {
  10. int i;
  11. for(i=1;i<=MAX;i++)
  12. {
  13. cout<<"Enter name: ";
  14. cin>>info[i].name;
  15. }
  16. cout<<endl;
  17. for(i=1;i<=MAX;i++)
  18. {
  19. cout<<"Stored name: "<<info[i].name<<endl;
  20. }
  21. }

Output :

C++ language simple structure program using define MAX

Next Update


We create a new YouTube channel (NightHawk) for gaming purpose like online games streaming or games review.

We need some time for make video tutorials (CodeX) so, stay with us and keep supporting and you know already we make a Collaboration with HackIsOn YouTube channel long time ago So, please Subscribe Our Channels

Protection died IPs active, this IP range is not allowed !