Skip to main content

Other Preprocessor commands


There are a handful more preprocessor commands which can largely be ignored by the beginner. They are commonly used in "include" files to make sure that things are not defined twice.

 NOTE : ‘true’ has any non zero value in C. ‘false’ is zero. 

 #undef         This undefines a macro, leaving the name free.

 #if                 This is followed by some expression on the same line. It allows
                      conditional compilation. It is an advanced feature which can be

                      used to say: only compile the code between ‘#if’ and ‘#endif’
                       if the value following ‘#if’ is true, else leave out that code altogether. This is      Different from not executing code—the code will not even be compiled.

 #ifdef     This is followed by a macro name. If that macro is defined then
                this is true.



#ifndef   This is followed by a macro name. If that name is not defined
                then this is true.

 #else      This is part of an #if, #ifdef, #ifndef preprocessor statement.

 #endif     This marks the end of a preprocessor statement.

 #line        Has the form:

 #line         constant ‘filename’This is for debugging mainly. This statement causes the com-
                  piler to believe that the next line is line number (constant) and
                  is part of the file (filename).

 #error        This is a part of the proposed ANSI standard. It is intended for
                   debugging. It forces the compiler to abort compilation.

 Read more about Prerocessor :-  Preprocessor

Labels:

Popular posts from this blog

C++ Program to find the sum, difference, product and quotient of two integers

#include <iostream.h> #include <conio.h> void main() {   clrscr();   int x = 10;   int y = 2;   int sum, difference, product, quotient;   sum = x + y;   difference = x - y;   product = x * y;   quotient = x / y;   cout << "The sum of " << x << " & " << y << " is " << sum << "." << endl;   cout << "The difference of " << x << " & " << "y <<  is " << difference << "." << endl;   cout << "The product of " << x << " & " << y << " is " << product << "." << endl;   cout << "The quotient of " << x << " & " << y << " is " << quotient << "." << endl;   getch(); }
Read more

Program of virtual piano

//////////////Tested And Created By C++/////////////////////////////// #include<stdio.h> #include<dos.h> #include<conio.h> #include<stdlib.h> #define SHOW 1 #define HIDE 2 union REGS input,output; class piano {  public:int BIGKEY,MIDKEY,back,border;     piano()//init constructor     {         BIGKEY=15;         MIDKEY=1;         back=7;         border=15;     } }color; void drawpiano(int x,int y); int check_xy(int x,int y); void BOX(int c,int r,int c1,int r1,int col); int initmouse(); void setupscreen(); void pointer(int on); void restrictmouse(int x1,int y1,int x2,int y2); void check_keys(int x,int y); void getmouse(int *button,int *x,int *y); float freq[7] = {130.81, 146.83, 164.81, 174.61,196, 220, 246.94 } ; int n=0,a=4,backcolor=2,exitcode=1; void showbar(int t) {  if(t>65) t=65;  if(t<1) t=1;  textcolor(15);  for(int q=0;q<=t;t++)  {     gotoxy(3+q,4);     cprintf("Û");  } } void main() {  int
Read more

Putimage function in c

putimage function outputs a bit image onto the screen. Declaration:- void putimage(int left, int top, void *ptr, int op); putimage puts the bit image previously saved with getimage back onto the screen, with the upper left corner of the image placed at (left, top). ptr points to the area in memory where the source image is stored. The op argument specifies a operator that controls how the color for each destination pixel on screen is computed, based on pixel already on screen and the corresponding source pixel in memory. c smiling face animation This animation using c draws a smiling face which appears at random position on screen. See output below the code, it will help you in understanding the code easily. C programming code #include<graphics.h> #include<conio.h> #include<stdlib.h>   main() { int gd = DETECT, gm, area, temp1, temp2, left = 25, top = 75; void *p;   initgraph(&gd,&gm,"C:\\TC\\BGI");   setcolor(YELLOW);
Read more