In this code, the FileStream class is used to open the input file (inputfile.txt) and read its contents. The bufferSize variable specifies the size of the buffer to be used for reading the file. In this example, a buffer size of 1 MB is used.

The while loop is used to read the input file in chunks of the specified buffer size. For each chunk of data, a new output file is created with a name in the format outputfile1.txt, outputfile2.txt, and so on. The fileCounter variable is used to keep track of the number of output files created.

The Write method of the output file stream is used to write the data to the output file. After the data has been written, the using block for the output file stream is closed, which ensures that the file is properly closed and flushed to disk.

By using the FileStream class in C#, you can split a file into multiple files with ease. This approach can be useful when you need to transfer large files over a network or when you need to process files in parallel on multiple systems.