[Web4lib] global variables versus local variables

[Vishwam Annam]

I use local variables, when I want to restrict them to be accessed only 
with in a subroutine or a class. I am not sure, whether declaring 
variables  as local makes your program more efficient or not, but it is 
good idea to use them for temporary or with-in subroutine(function) 
computations. 

About  the for loop, if you have one like, for (int i=0;i<10;i++) this 
doesn't define "i" 10 times, it just increments it's value each time by 
one. If you have some thing like  for (int i=0;i<10;i++)  { int j=0; } 
then "j" is defined and initialized to 0 ten times.

I use global variables if I want to use their values anywhere throughout 
my program.

Vishwam
Wright State University Libraries

Karen Coyle wrote:

> When I was learning programming that had local and global variables, 
> the local variables were billed as being more "safe" because other 
> routines could not inadvertently modify or delete them. You chose 
> local or global depending on the role of the data element in relation 
> to the sub-routines, not based on efficiency. And with the speed of 
> today's computers, the difference in efficiency between a global and a 
> local variable may not be significant for most applications.
>
> Others can undoubtedly explain this better than I.
>
> kc
>
> John Fitzgibbon wrote:
>
>> Hi,
>>
>> When programming and when writing scripts, we are encouraged to use
>> variables that are local in scope whenever we can.
>>
>> However, defining a variable within a sub-routine, as in VbScript, means
>> the variable is defined every time the sub-routine is run whereas
>> defining it outside the sub-routine means the variable is defined only
>> once. Why is it more efficient to define a variable within a
>> sub-routine?
>>
>> Also, defining a variable within a loop causes the variable to be
>> defined afresh with each instance of the loop. Again this appears
>> inefficient but is generally done when a 'for loop' is run in
>> JavaScript.
>>
>> I don't doubt that local variables have their uses; I'm simply seeking
>> an explanation.
>>
>> Regards
>> John
>>
>> John Fitzgibbon
>>
>> John Fitzgibbon
>>
>> Galway Public Library
>> Island House
>> Cathedral Square
>> Galway
>> Ireland
>>
>> p: 00 353 91 562471
>> f: 00 353 91 565039
>> w: http://www.galwaylibrary.ie
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