Thread: Multi line macro help

I cannot find any good info on how to setup multi line macros. The problem I am having is that I need to use only macros (no functions) to compute factorials. When I use functions the code works but when I try to use macros I keep getting parse errors(it points to the macro I am using as the problem).

Code:

#include<stdio.h>
#include<math.h>
#define fact(x) do {    \
int factorial=1;        \
int k=1;                \
factorial=factorial*k;  \
k++;                    \
} while (k<=n)

#define comb(answer)(result/(input*last))
//int fact(int n);
main()
{
int n,k,x,result,diff,input,answer,last;
printf("Please enter a value for n \n");
scanf("%i",&n);
printf("Please enter a value for k \n");
scanf("%i",&k);
if (n<k)
  printf("N must be larger than or equal to K \n");
else 
  {
  result=fact(n);
  input=fact(k);
  diff=n-k;
  last=fact(diff);  
  printf("The combination of %i things taken %i at a time is %i \n",n,k,comb(answer)); 
  } 
return 0;
}


//int fact(int n)
//{
//	int k;
//	int factorial=1;
//	for(k=1; k<=n; k++)
//	{
//		factorial=factorial * k;
//	}
//return factorial;		
//}

I left the function in there so people can understand what I am trying to achieve. If anyone has any advice or can point me to some resources that discuss how to set up multi line macros I would really appreciate it. Thank you in advance.

So you have, after replacement, result = do stuff. do does not yield a numeric answer that can be assigned to result.

Thank you very much for replying. Should I use a for loop instead? I guess I am kind of stuck on how this type of macro works.

It's just text substitution, like all macros. The text you supply is literally pasted in the place of your "function call". So it must be a bit of code that you would expect to see on the right-hand side of an equals sign.

(EDIT: Or alternatively, you can just do fact(k,n) where the first variable gets assigned the value of n!.)

I am really struggling to grasp this problem. There has to be a loop somewhere. Either in the macro or main and I think that is where I am getting lost because I don't know how to set up a loop in the macro and in main I think I would need a separate loop for each input if I define it like this

Code:

#define fact(k,n)(factorial=factorial*k)

I know that factorial = x(x-1)(x-2)...x number of times or x(x+1)(x+2)...x number of times but I do not know how set that up without using a function. Any more pointers would be greatly appreciated.

So you can set it up as a loop if you want, that's fine. You will just have to take the answer as a parameter, and at the end of your loop, do k = answer or whatever.

You are right. I could only find examples of do while loops and I have been searching for a long time. I have been trying to not use a loop in the macro like this

Code:

 #include<stdio.h>
#include<math.h>
#define fact(x)(factorial=factorial*k)
#define comb(answer)(result/(input*last))
main()
{
int n,k=1,x,result,diff,input,answer,last,factorial=1;
printf("Please enter a value for n \n");
scanf("%i",&n);
printf("Please enter a value for k \n");
scanf("%i",&k);
if (n<k)
  printf("N must be larger than or equal to K \n");
else 
  {
  diff=n-k;
  for(k=1; k<=n; k++)
	{	
  result=fact(n);
  	}
  for(k=1; k<=n; k++)
	{	
  input=fact(k);
  	}
  for(k=1; k<=n; k++)
	{	
  last=fact(diff);
  	}      
  printf("%i  \n",result);
  printf("%i \n",input);
  printf("%i \n",last);
  printf("The combination of %i things taken %i at a time is %i \n",n,k,comb(answer));  
  } 
return 0;
}

but it is not working correctly. The first loop is gets the right answer but the next loops don't so I am not sure if this is even a correct setup. I feel like I am on the right track though so hopefully something will click soon.

I have to do it this way. I would rather use functions but this is what the instructor wants. Here is what i have so far

Code:

#include<stdio.h>
#include<math.h>
#define fact(x) for(j=(x-1); j>=0; j--) 		\
	{					\
		x=x * j;			\
	}					\
	return x;		
	
#define comb(answer)(result/(input*last))
main()
{
int n,k,j,x,result,diff=n-k,input,answer,last,ret_val;
printf("Please enter a value for n \n");
scanf("%i",&n);
printf("Please enter a value for k \n");
scanf("%i",&k);
if (n<k)
  printf("N must be larger than or equal to K \n");
else 
  {
  fact(n);
  fact(k);    
  fact(diff);    
  printf("The combination of %i things taken %i at a time is %i \n",n,k,comb(answer));   
  } 
return 0;
}

It compiles. But when I enter the second number the program hangs. So I am getting even closer. Thank you for your suggestion. I am going to give it a try.

What makes this problem is just that; most people are against using macros so it is very difficult to find any resources or help on the subject. So far I have a pretty good grasp on C programming but this problem is killing me. In my instructors defense he has put out that macros should not be used. He justs wants us to know what they are and why they shouldn't be used.

If you look at my first post I left the original working code with a function in but I // it.The assignment is to remove the function from the code and use two macros. One to compute the factorial and one that computes n!/k!(n-k)!. What I don't understand is that once I remove the function with the loop where does the loop go? I have tried a lot of different approaches but so far no luck. I know I need three loops; one for n!,k! and (n-k)! so I think having a loop in the macro makes the most sense. I have tried using 3 for loops in main but that didn't turn out. If you have any more suggestions I would greatly appreciate it.