c# - which form of property declaration is more appropriate? -

it's been while simple question disturbing me , i've seen 2 form of declaring properties , , wondering what's different , there reason makes me prefer 1 ?

1st form :

public int age { get; set; } 

2nd form :

private int _age; public int age {     { return _age; }     set { _age = value; } } 

i've used second form , i've seen msdn tutorial talks 2nd form , i'm little confused here , 1 preferred ?

the first form "new". find lot of "old" code contains second form.

today, using modern versions of c#, reason use second form hook more logic inside getter or setter.

for instance:

private int mypropertyvalue;  public int myproperty {          {         return mypropertyvalue;     }     set     {         if (value >= 0 && value <= 100)         {             mypropertyvalue = value;         }         else         {             // throw exception here.         }     } }