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COMMON /USELESS/ KDO K=1,1000 IF (K .EQ. 1) CALL AUXENDDO

In this example, K has been declared as a COMMON variable. It is used only as a do-loop counter, so there really is no reason for it to be anything but local. However, because it is in a COMMON block, the call to AUX forces the compiler to store and reload K each iteration. This is because the side effects of the call are unknown.

So far, it looks as if we are preparing a case for huge main programs without any subroutines or functions! Not at all. Modularity is important for keeping source code compact and understandable. And frankly, the need for maintainability and modularity is always more important than the need for small performance improvements. However, there are a few approaches for streamlining subroutine calls that don’t require you to scrap modular coding techniques: macros and procedure inlining.

Remember, if the function or subroutine does a reasonable amount of work, procedure call overhead isn’t going to matter very much. However, if one small routine appears as a leaf node in one of the busiest sections of the call graph, you might want to think about inserting it in appropriate places in the program.

Macros

Macros are little procedures that are substituted inline at compile time. Unlike subroutines or functions, which are included once during the link, macros are replicated every place they are used. When the compiler makes its first pass through your program, it looks for patterns that match previous macro definitions and expands them inline. In fact, in later stages, the compiler sees an expanded macro as source code.

Macros are part of both C and FORTRAN (although the FORTRAN notion of a macro, the statement function , is reviled by the FORTRAN community, and won’t survive much longer). The statement function has been eliminated in FORTRAN 90. For C programs, macros are created with a #define construct, as demonstrated here:


#define average(x,y) ((x+y)/2) main (){ float q = 100, p = 50;float a; a = average(p,q);printf ("%f\n",a); }

The first compilation step for a C program is a pass through the C preprocessor, cpp . This happens automatically when you invoke the compiler. cpp expands #define statements inline, replacing the pattern matched by the macro definition. In the program above, the statement:


a = average(p,q);

gets replaced with:


a = ((p+q)/2);

You have to be careful how you define the macro because it literally replaces the pattern located by cpp . For instance, if the macro definition said:


#define multiply(a,b) (a*b)

and you invoked it as:


c = multiply(x+t,y+v);

the resulting expansion would be x+t*y+v — probably not what you intended.

If you are a C programmer you may be using macros without being conscious of it. Many C header files ( .h ) contain macro definitions. In fact, some “standard” C library functions are really defined as macros in the header files. For instance, the function getchar can be linked in when you build your program. If you have a statement:


#include<stdio.h>

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, High performance computing. OpenStax CNX. Aug 25, 2010 Download for free at http://cnx.org/content/col11136/1.5
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