How to define a table when you have the column names in a file.

I am able to extract the column names from the file into an array list. What to do next to create a table with these columns.
Secondly i have a data set taken from a file. All the data is initially string. Now i have to convert the ones corresponding to numeric to numeric real to real char to char n string to string respectively. This can done by analysing all the rows of the columns.
It can be done using the fact that real(string initially) will have a . followed by  no.. But is there any other way or function defined to do so??