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Odd function declaration in Tower of Hanoi Solution

Posted on 2004-10-31
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Last Modified: 2010-04-15
Hi,

I was recently looking for a recursive solution to the "Tower of Hanoi" problem, and I came across this:

void move(n, A, C, B)
     int n,A,B,C;
{
  if (n==1)
    printf("Move from %d to %d.\n",A,C);
  else {
    move(n-1,A,B,C);
    move(1,A,C,B);
    move(n-1,B,C,A);
  }
}
 
int main(void) {
  move(4,1,3,2);

  return 0;
}

I understand the solution, what I don't understand is the function declaration!  Why are n, A, B, and C declared just outside of the function prototype, and where is the function prototype?

Raydot.
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Question by:Raydot
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4 Comments
 
LVL 22

Expert Comment

by:grg99
ID: 12456716
This is an old-style function declaration.  It took the C Wizards about a decade to figure out it made more sense to declare the types alongsides the parameters.  

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LVL 3

Author Comment

by:Raydot
ID: 12462818
"declare the types alongsides the parameters" -- huh?  

0
 
LVL 22

Accepted Solution

by:
grg99 earned 200 total points
ID: 12466103
The original C syntax was:

<function type> <function name> ( <param name1>, <param name2>, .... )   <param 1 type >  name1,  <param 2 type>  name2, ...


in other words:   void move(n, A, C, B)    int n,A,B,C;

----------------------------------------
this was mighty silly and repetetive syntax, just like the old FORTRAN way of declaring parameters.

Somewhere along the line the parameter syntax was loosened up so you
could use the newer syntax:   void move( int n, int a, int c, int b );
This also made it possible to pre-declare the function and parameter types.
------------------------------------------------------

I would change the functions to use the new-style headers.  The semantics should be just the same.


 
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LVL 3

Author Comment

by:Raydot
ID: 12474591
What the problem was is that the program didn't work when I converted it to the "new" function declaration, but that turned out to be because I re-wrote the prototype as

void move(int n, int A, int B, int C)

and not

void move(int n, int A, int, C, int B)

...and hence my confusion.  Thanks for your help.
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