c# - Returning a date from a class -

what want have user enter date , have class returns last day of month. so, i've put in class module:

public static class stringextensions {     public static datetime lastdayofmonth(datetime mydate)     {         datetime today = mydate;         datetime eom = new datetime(today.year,today.month,                            datetime.daysinmonth(today.year,                            today.month));             return eom;     } } 

in code-behind, have this:

datetime ldom = stringextensions.lastdayofmonth(txtcit.text); 

i've tried hard-coding date like:

datetime ldom = stringextensions.lastdayofmonth('1/12/2016'); 

i'm getting these errors:

error 14 best overloaded method match 'clientdpl.stringextensions.lastdayofmonth(system.datetime)' has invalid arguments

and

error 15 argument 1: cannot convert 'string' 'system.datetime'

can see i'm doing wrong?

as @mason pointed out in comment, better way use datetime extension method similar to:

public static class datetimeextensions {     public static datetime lastdayofmonth(this datetime date)     {         datetime eom = new datetime(             date.year,date.month,             datetime.daysinmonth(                 date.year,                 date.month             )         );          return eom;     } } 

can used like:

console.writeline(datetime.now.lastdayofmonth()); 

see in action at:

https://dotnetfiddle.net/59oj7c