c# - Conditionally creating new collections with output parameters -

this program purely illustrative purposes. wanted take integer input , if greater zero, create arraylist integer in arraylist. tried numerous (incorrect) ways , settled on see below. however, don't looks of it.

using system; using system.collections.generic; using system.linq; using system.text; using system.collections;      class program     {         static void main(string[] args)         {             console.write("enter in number of size of arraylist want: ");             int arraysize = int.parse(console.readline());             if (arraysize > 0)             {                 arraylist newlist = createlist(arraysize,out newlist);                 newlist.add(arraysize);                 console.writeline("the size of array {0}",newlist.count);                 console.readline();             }             else             {                 console.writeline("you did not create arraylist");             }             console.writeline("here can't access array");             console.readline();             }         public static arraylist createlist(int x,out arraylist outlist)         {             arraylist al = new arraylist(x);             outlist= al;             return outlist;          }     } 

my thought process if user decided on action program wouldn't create arraylist save resources (silly example considering example, know) . however, still have initialize arraylist in main method, , if take out line newlist.add(arraysize) program runs output of 0 if user enters number greater 0. there way make input greater 0 result in arraylist that's ready go element added? if commented out line newlist.add(arraysize) program still print out size of arraylist 1 (provided number greater 0)

in example number of elements maximum of 1, , not number user might enter.

there's lot of things going wrong here.

firstly, can't add size of list. it's initialised in constructor, , grows , shrinks add , remove elements.

so line:

newlist.add(arraysize); 

is misleading , not want. either want add element (in case variable name misleading) or want set array's size or capacity, in case code isn't doing want.

there difference between list's size , capacity should aware of:

• size number of elements in array.
• capacity size of list's underlying array, equal or greater list's size @ point in time.

this why call count returning 0 when you've initialised list other value. count refers number of items in list, not length of internal array. want call capacity property instead:

console.writeline("the size of array {0}", newlist.capacity); 

lists (arraylist , list) use array's internally, of fixed size. capacity refers length of array. , when add new element list array full, list's add method creates new array double length of old array, copies elements larger array, appends new value @ end, , discards old array.

so in short, function:

public static arraylist createlist(int x,out arraylist outlist) {     arraylist al = new arraylist(x);     outlist= al;     return outlist; } 

is okay, though redundant in should either use out parameter or return list, not both. case, like:

public static void createlist<t>(int capacity, out list<t> list) {     list = new list<t>(capacity); } 

even though it's pretty pointless method stands.