#define

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

Example :

/* Description: Area of circle use define in C++ language */ #include<iostream> #define PI 3.14159 using namespace std; int main() { int r=10; float cir; cir=PI*(r*r); cout<< "Area of circle: " <<cir <<endl; }

Output :

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 :

/* Description: simple structure program using define MAX in C++ language */ #include<iostream> #define MAX 2 using namespace std; struct data{ char name[20]; }info[4]; int main() { int i; for(i=1;i<=MAX;i++) { cout<<"Enter name: "; cin>>info[i].name; } cout<<endl; for(i=1;i<=MAX;i++) { cout<<"Stored name: "<<info[i].name<<endl; } }

Output :