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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

An investment account was opened with an initial deposit of $9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
Kala Reply
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
Akash
College algebra is really hard?
Shirleen Reply
Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
Carole
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
I rally confuse this number And equations too I need exactly help
salma
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salma
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
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Tamia
hii
Uday
hi
salma
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
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Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
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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