This document provides an introduction to preprocessor directives in C++. It defines preprocessor directives as instructions for the preprocessor, not actual program statements. Several common preprocessor directives are listed, including #define, #include, #if, #endif, and #else. The #define directive is used to define macros by associating an identifier with a replacement text. An example demonstrates using #define to create constants for PI and then printing PI, pi, and their product. The document also shows how #define can be used to define a macro function called square() that squares its argument.

2. Introduction to C ++

3. DEFINITION
Preprocessor directives are
not program statements but
directives for
PREPROCESSOR

4. AVAILABLE
•
•
•
•
•
#define
#undef
#ifdef
#ifndef
#error
•
•
•
•
•
#pragma
#if
#endif
#else
#elif

5. #define
#define identifier replacement
#define PI 3.14159
const float PI = 3.14159;

6. #include<iostream.h>
#define PI 3.14159
void main(void)
{
const float pi = 3.14159;
EXAMPLE
PI: 3.14159
pi: 3.14159
pi*PI: 9.86958
cout<<"PI: "<< PI <<endl<<endl;
cout<<"pi: "<< pi << endl << endl;
cout<<"pi*PI: "<<pi*PI<<endl<<endl;
} // main function ends here

7. DEFINING MACROS
#define m-identifier replacement
#define square(x) (x)*(x)
double square(double x){return x*x;}

8. EXAMPLE
#include<iostream.h>
Square of 9 is: 81
Square of 9+1 is: 100
#define square(x) (x)*(x)
double sqr(double x){return x*x;} Square of 9 is: 81
void main(void){
int value = 9;
cout<<"Square of "<<value<<" is: "<<square(value)<<endl;
cout<<"Square of "<<value<<"+1 is: "<<square(value+1)<<endl;
cout<<"Square of "<<value<<" is: "<<sqr(double(value));
}// main function ends here

9. OUTPUT
Square of 9 is: 81
Square of 9+1 is: 100
Square of 9 is: 81

10. Questions
&
Answers

11. Thanks