Thread: Macros question

Why are you using macros? What's the point?

Code:

switch( task )
{
    case '+': value = value_1 + value_2; break;
    case '/': value = value_1 / value_2; break;
    case '*': value = value_1 * value_2; break;
    case '-': value = value_1 - value_2; break;
}

Seriously, what is the purpose of you making macros? No, you cannot have a macro that takes just the two arguments to do the math on and have it do both the division or multiplication. It doesn't work that way. You have to specify what task you want it to do. Make one to multiply and one to divide.

Seriously though, I see no point in even bothering with macros.

Quzah.
}

>No, you cannot have a macro that takes just the two arguments to do the math on and have it do both the division or multiplication.
With a clever hack you probably could come up with something, but a more sane way would be to have a three argument macro:

Code:

#include <stdio.h>

#define CALC(x,op,y) ((x) op (y))

int main ( void )
{
  printf ( "%d\n", CALC ( 1, +, 1 ) );
  printf ( "%d\n", CALC ( 5, -, 2 ) );
  printf ( "%d\n", CALC ( 2, *, 2 ) );
  printf ( "%d\n", CALC ( 10, /, 2 ) );

  return 0;
}

This is questionable style though, I wouldn't use it in production code unless there were no other way.

-Prelude

The requirement is a very odd one. You should not have a two arguement macro when you really need three. It just is bad form. This will do the trick for you though:

Code:

struct values
{
    long int value_1;
    long int value_2;
};


#define MULTIPLYDIVIDE(x,y)  y=='*' ? \
    (x.value_1 * x.value_2)  : \
    (x.value_1 / x.value_2)

Usage of the macro would be:

struct values mydata;
mydata.value_1 = something;
mydata.value_2 = somethingelse;

sum = MULTIPLYDIVIDE( mydata, '/' );

There. You basicly pass it three values by using a structure. You could create another structure for floating point values , with the same value 'value_1', and 'value_2' respectivly, so the macro works right.

Hey, I didn't see in the instructions anything saying you cannot use structures.

I'm sure there's some other messed up hack you could use to do a 2 argument macro, but you really need three arguments to do it "right".

Quzah.

>But my teacher said that is other way.
Your teacher is either very sadistic, or an idiot. Really the only workable solution with two arguments that I can think of right now is to use an array or struct to hold both values, then pass the operation as the second argument:

Code:

#include <stdio.h>
#include <math.h>

#define MULTIPLYDIVIDE(x,y) ((x[0]) y (x[1]))
#define TRIG(type,angle)    (type)( (angle) )
#define ADDSUBTRACT(x,y)    ((x[0]) y (x[1]))
#define MODULUS(x,y)        ((x) % (y))

int main ( void )
{
  int a[] = {6, 3};

  printf ( "%d\n", MULTIPLYDIVIDE ( a, * ) );
  printf ( "%d\n", MULTIPLYDIVIDE ( a, / ) );

  return 0;
}

-Prelude

Code:

#include <stdio.h>
#include <math.h>

#define MULTIPLYDIVIDE( x, y ) (int)( ( x ) * ( y ) )
#define ADDSUBTRACT( x, y ) ( ( x ) + ( y ) )
// The * atan( 1 ) / 180.0 part converts to radians. atan(1) == pi.
#define TRIG( type, angle ) (int)( type ( (double)( angle ) * ( atan( 1 ) / 180.0 ) ) )
#define MODULUS( x, y ) ( ( x ) % ( y ) )

int main( void ) {
	int a = 6;
	int b = 3;
	// a / b = a * ( 1 / b )
	printf( "%d\t%d\n", MULTIPLYDIVIDE( (double)a, 1.0 / (double)b ), MULTIPLYDIVIDE( (double)a, (double)b ) );
	return 0;
}

Looks work well..... Thx....

Originally posted by Dave_Sinkula
How about something like this?

Code:

#include <stdio.h> 

#define ADDSUBTRACT(x,y)      ( (x) + (y) )
#define MULTIPLYDIVIDE(x,y)   ( (x) * (y) )

int main(void)
{
   double a = 1.23, b = 4.56;
   printf("%f + %f = %f\n", a, b, ADDSUBTRACT(a, b));          /* add */
   printf("%f - %f = %f\n", a, b, ADDSUBTRACT(a, -b));         /* subtract */
   printf("%f * %f = %f\n", a, b, MULTIPLYDIVIDE(a, b));       /* multiply */
   printf("%f / %f = %f\n", a, b, MULTIPLYDIVIDE(a, 1.0 / b)); /* divide */
   return(0);
}

/* my output
1.230000 + 4.560000 = 5.790000
1.230000 - 4.560000 = -3.330000
1.230000 * 4.560000 = 5.608800
1.230000 / 4.560000 = 0.269737
*/