How do I convert a string to a long integer type

Example converting a string "123456789987654321" to integer value as 123456789987654321.

For a long, I think you'll want Convert.ToInt64( "1234567890987654321" );

Use the Convert class: http://msdn.microsoft.com/en-us/library/dsfy6sz9%28v=VS.100%29.aspx