Introduction to Programming Lecture 23 Preprocessors and Header files

Today’s Lecture Preprocessor Directives Header Files Macros

Preprocessor

#include <iostream.h>

#

#include #include <iostream.h> #include <stdlib.h> #include <fstream.h> #include <stream.h>

5:10 to 5:23

5:24 to 5:41

Re-locatable Executable

MyHeader.h

#include “MyHeader.h”

#include <iostream.h>

#define

#define PI 3.141592

Preprocessor Directives #if #else #endif #elif #ifdef #ifndef #error

Preprocessor Directives #ident #import #line #machine #system #warning

Example #ifdef PI

# define PI # ifdef PI

# define DEBUG # ifdef DEBUG

Conditional Compilation Macro Translation

#undef DEBUG

#include <conio.h>       #include <conio.h> Consol Input Output  

#include <conio.h> #include <conio.c>

int getche ( ) ;

Get Character With Echo

#ifdef __cplusplus extern "C" { #endif - - }

Macro

Example 1 #define SQUARE ( X ) X * X main ( ) { int i = 5 , j ; : } i * i ; SQUARE ( i ) ;

Example 2 #define SQUARE ( X ) X * X main ( ) { int i = 5 , j = 10 , k ; : k = } i + j * i + j ; SQUARE ( i + j ) ;

Example 3 #define SQUARE(X) (X)*(X) main ( ) { int i = 5 , j = 10 , k ; k = } SQUARE ( i + j ) ; ( i + j ) * ( i + j ) ;

Overhead

Code Bloat

Example 4 #define PI 3.14159 #define CIRCLEAREA ( X ) main ( ) { float radius ; cout << “ Enter radius of Circle Area : ” ; cin >> radius ; cout << “ Area of Circle Area is ” << } ( ( PI ) * ( X ) * ( X ) ) PI * X * X CIRCLEAREA ( 2 * radius ) ; CIRCLEAREA ( radius ) ; ( ( PI ) * ( radius ) * ( radius ) ) ;

Header Files

Header File #include <iostream.h> #include <stdlib.h> #include <stdio.h> #include <string.h>

In Next Lecture Memory Allocation