Can some help me with the syntax, ADo.net C# dataset query

[khawar]

hi every body
i need help
i have a dataset called ds, which contains a table called
login_table, which contains three columns, namely (login,
password, email).
Now the question is that, can someone translate this query
in correct syntax of C#:
"select email from login_table where login='john'"

i want some thing like following, and i don't know the
correct syntax:
string email=ds."select email from login_table where
login='john'"

basically save the scalar(string in this case) value to an
string called email.

all help will be appriciate, help the needy coder
bye