You can use any valid C data type in your C code. However, variables that correspond to terminals must be of one of the following data types: signed and unsigned integers, characters (8-bit integers), doubles, Booleans, strings, and 1-dimensional arrays of any of the preceding types.
By default, LabVIEW adapts the data type of the input to the data type of the terminal to which you wire the input. The default data type for an output is double.
To interact with string and array terminals, use the following C node functions to get and set the size of the array: