SQL Search :: Generating Dynamic Query

I have a table named "Persons"  which has the following columns [ Name ,Age, City]. I have a Windows app which has  3 textboxes for each column. My requirement is when I enter only name and enter the search button, I need result similar to this query.
     
select * from persons where name like '@tbname%'
when I enter only age and enter the search button, I need result similar to this query.
select * from persons where age =@tbage
when I enter name and city, I need result similar to this query.
select * from persons where name like '@tbname%' and city like '@tbcity%'

If I don't enter any fields and enter the serach button,  I need result similar to this query.

select * from persons for these 3 fields I might give any combination as above. But how can  I have a single query with all these combinations. I want a single query capable of doing this. I cannot have query like this, select * from persons where name like 'tbname%' and city like 'tbcity%' and age =@age

Because if I give only name,  city is considered as null nad age is considered as 0 and I get empty result. I cannot have Stored proc and I cannot do much in C# like using "selectqueryBuilder" etc. I need pure SQL query.