Why did I get the compile error Use of unassigned local variable

Question

My code is the following int tmpCnt    if  name     quot Dude quot        tmpCnt       Why is there an error  quot Use of unassigned local variable tmpCnt quot   I know I didn t explicitly initialize it  but due to Default Value Table a value type is initialized with 0 anyway  The reference also reminds me   Remember that using uninitialized variables in C  is not allowed   But why do I have to do it explicitly if it s already done by default  Wouldn t it gain performance if I wouldn t have to do it

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IEnumerable lt DateTime  gt   getCurrentHolidayList    this will not initailize   Assign value  getCurrentHolidayList  inside the loop  foreach  HolidaySummaryList  holidayItem in  holidayDetailsList                                if   holidayItem CountryId    Countryid                                   getCurrentHolidayList    holidayItem Holiday                                                         After your are passing the local varibale to another method like below   It throw error use of unassigned variable   eventhough nullable mentioned in time of decalration   var cancelRescheduleCondition   GetHolidayDays  item ServiceDateFrom   getCurrentHolidayList     if you mentioned like below  It will not throw any error   IEnumerable lt DateTime  gt   getCurrentHolidayList  null

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Local variables aren t initialized   You have to manually initialize them   Members are initialized  for example   public class X       private int  tmpCnt     This WILL initialize to zero             But local variables are not   public static void SomeMethod         int tmpCnt      This is not initialized and must be assigned before used               So your code must be   int tmpCnt   0    if  name     Dude        tmpCnt        So the long and the short of it is  members are initialized  locals are not   That is why you get the compiler error

User · Answer

Default assignments apply to class members  but not to local variables  As Eric Lippert explained it in this answer  Microsoft could have initialized locals by default  but they choose not to do it because using an unassigned local is almost certainly a bug

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See this thread concerning uninitialized bools  but it should answer your question   Local variables are not initialized unless you call their constructors  new  or assign them a value

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While value types have default values and can not be null  they also need to be explicitly initialized in order to be used  You can think of these two rules as side by side rules  Value types can not be null   the compiler guarantees that  If you ask how  the error message you got is the answer  Once you call their constructors  they got initialized with their default values  int tmpCnt     Not accepted int tmpCnt   new Int       Default value applied tmpCnt   0

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The default value table only applies to initializing a variable   Per the linked page  the following two methods of initialization are equivalent     int x   0  int x   new int      In your code  you merely defined the variable  but never initialized the object

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Local variables don t have a default value  They have to be definitely assigned before you use them  It reduces the chance of using a variable you think you ve given a sensible value to  when actually it s got some default value

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Local variables are not automatically initialized  That only happens with instance-level variables   You need to explicitly initialize local variables if you want them to be initialized  In this case   as the linked documentation explains  either by setting the value of 0 or using the new operator   The code you ve shown does indeed attempt to use the value of the variable tmpCnt before it is initialized to anything  and the compiler rightly warns about it

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The following categories of variables are classified as initially unassigned    Instance variables of initially unassigned struct variables  Output parameters  including the this variable of struct instance constructors  Local variables   except those declared in a catch clause or a foreach statement    The following categories of variables are classified as initially assigned    Static variables  Instance variables of class instances  Instance variables of initially assigned struct variables  Array elements  Value parameters  Reference parameters  Variables declared in a catch clause or a foreach statement

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A very dummy mistake  but you can get this with a class too if you didn t instantiate it  BankAccount account  account addMoney 5    The above will produce the same error whereas  class BankAccount       int balance   0      public void addMoney int amount                balance    amount           Do the following to eliminate the error  BankAccount account   new BankAccount    account addMoney 5

[c#] Why did I get the compile error "Use of unassigned local variable"?

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