The actual error message contains a lot more information than that....

Ray L.

there are things in your code that don't make sense like:

bool done which is then re-declared as float!!!!!

anyway '' is a 'void' function ie it does not return anything... hence your error.

if you change the initial 'if' statement to so something like this, it compiles:

  if (radio.available())
  {, 1);

The function does not return a value.
You can’t assign the value it doesn’t return to a variable.

If you search through the RF24.h file you are including, you will see that .read is a void function, it does not return a value.

void RF24::read( void* buf, uint8_t len )
  // Fetch the payload
  read_payload( buf, len );

  //Clear the two possible interrupt flags with one command
  write_register(NRF_STATUS,_BV(RX_DR) | _BV(MAX_RT) | _BV(TX_DS) );

It's the classical case of an old-library-sample-code used with the newer and better library.