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brad sue · Apr 22nd, 2006, 6:03 PM

Hi I would like to check if an array of interger is empty( fortran 77).
my strategy is to set all the elements equal to zero. then to check if the array is empty I set a counter that count the number of zeros. if this number is equal with tha length of the array then the array is empty.

(Toggle Plain Text)

do 11 k=1,10
	listonline(k)=0
11	continue

else if(option.EQ.'PL') then
      
          do 81 p=1,j-1,1
              if(listonline(p).EQ.0) then
                  hh=hh+1 
           end if	
81        continue
       write(6,*)'number of zeros',hh

When I try to print hh, it gives me 0.

Is there another way to check for empty array( of interger)

Thank you
B.

Jimbo · Apr 22nd, 2006, 6:13 PM

What if 0 is a valid data value?

brad sue · Apr 22nd, 2006, 6:32 PM

Quote:

Originally Posted by Jimbo

What if 0 is a valid data value?

Yes this is what I though but I dont see something else to do!

But suppose that 0 is not an elligible value in the array, why does my approach not work?
B.

grumpy · Apr 22nd, 2006, 9:48 PM

You basically need to define some condition that means the array is empty.

One way is to pick a value that says "this cell is empty" and check how many elements in the array have that value. Your approach of using zero as an invalid value is a particular case of this. Naturally, with this approach, you need to initialise the array before trying to use it, and I'll bet that's causing your code "not to work" --- as with many programming languges, an array in Fortran is not initialised to zero except in special cases, and you're probably assuming the array starts life with zero values.

Another way is to separately keep track of the number of non-empty elements, and shuffle elements in the array whenever you add or remove an element to it. That way you know that the elements 1 through to n (where, if n is positive, it is the number of valid elements) are not empty.

Neither approach is perfect. For example, in a scenario where you wish to add a new valid cell, the first method is probably less efficient than the first as it requires searching the array to find a slot, which is not necessarily efficient, while the method just adds a value to the end and increments a count. However, in another scenario where you wish to remove a cell, the first scenario is more efficient as you simply set the value in a cell to be your invalid value compared with shuffling elements around.

Apr 22nd, 2006, 6:03 PM	#1
brad sue Hobbyist Programmer Join Date: Mar 2006 Posts: 120 Rep Power: 3	empty array Hi I would like to check if an array of interger is empty( fortran 77). my strategy is to set all the elements equal to zero. then to check if the array is empty I set a counter that count the number of zeros. if this number is equal with tha length of the array then the array is empty. (Toggle Plain Text) do 11 k=1,10 listonline(k)=0 11 continue else if(option.EQ.'PL') then do 81 p=1,j-1,1 if(listonline(p).EQ.0) then hh=hh+1 end if 81 continue write(6,)'number of zeros',hh do 11 k=1,10 listonline(k)=0 11 continue else if(option.EQ.'PL') then do 81 p=1,j-1,1 if(listonline(p).EQ.0) then hh=hh+1 end if 81 continue write(6,)'number of zeros',hh When I try to print hh, it gives me 0. Is there another way to check for empty array( of interger) Thank you B.

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Apr 22nd, 2006, 6:13 PM	#2
Jimbo Battle Programmer Join Date: Feb 2006 Location: Bellevue, WA, USA Posts: 770 Rep Power: 3	What if 0 is a valid data value?

Apr 22nd, 2006, 9:48 PM	#4
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	You basically need to define some condition that means the array is empty. One way is to pick a value that says "this cell is empty" and check how many elements in the array have that value. Your approach of using zero as an invalid value is a particular case of this. Naturally, with this approach, you need to initialise the array before trying to use it, and I'll bet that's causing your code "not to work" --- as with many programming languges, an array in Fortran is not initialised to zero except in special cases, and you're probably assuming the array starts life with zero values. Another way is to separately keep track of the number of non-empty elements, and shuffle elements in the array whenever you add or remove an element to it. That way you know that the elements 1 through to n (where, if n is positive, it is the number of valid elements) are not empty. Neither approach is perfect. For example, in a scenario where you wish to add a new valid cell, the first method is probably less efficient than the first as it requires searching the array to find a slot, which is not necessarily efficient, while the method just adds a value to the end and increments a count. However, in another scenario where you wish to remove a cell, the first scenario is more efficient as you simply set the value in a cell to be your invalid value compared with shuffling elements around.

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