nc_varinq_datatype returns the data type of a variable when given its ID.
datatype is the data type of the variable with the ID varid and is one of the following:
|NC_CHAR||for representing text strings as arrays of ASCII characters|
|NC_FLOAT||32-Bit IEEE floating-point|
|NC_DOUBLE||64-Bit IEEE floating-point|
If an error occurs, datatype is -1.
Identifies the netCDF file.
varid is the ID of the variable.