c# - 'int' never equal to null for 'char' variables -

can answer me - why warning "the result of expression 'false' since value of type 'int' never equal 'null' of type 'int?'"

here code

    private char classletter;     public char classletter     {         { return classletter; }         set          {             if (classletter == null)             {                 classletter = value;                 raisepropertychanged("classletter");             }             else throw new argumentoutofrangeexception();         }     } 

if use code no warning comes in

    private char classletter;     public char classletter     {         { return classletter; }         set          {             if (classletter.tostring() == null)             {                 classletter = value;                 raisepropertychanged("classletter");             }             else throw new argumentoutofrangeexception();         }     } 

in short question this

how can int warning given char variable?

edit: 'char' should hold latin or cyrillic letter, no special symbols , no numbers allowed. how should filtered?

in first case, classletter of type char, can never null because it's value type; need of type char?. comparing classletter == null doesn't make sense, compiler says.

in second case, imagine classletter 'x'. when doing classletter.tostring() "x", can compared null because reference type. again, not want because classletter.tostring() never null.

if want allowing set value once, can this:

private char? classletter = null; // make nullable public char classletter {     {         if(classletter == null) { // if don't have value yet             // something, throwing exception         }else{ // if have value             return classletter.value; // here return char, not char?         }     }     set      {         if (classletter == null) {             classletter = value;             raisepropertychanged("classletter");         }         else throw new argumentoutofrangeexception();     } }