Change of type and bitSet

Projects Programming
1

Hello everyone , i am new in this forum and have two litte question , first of all i am reading "ARDUINO APLICACIONES EN ROBOTICA, MECATRONICA E INGENIERIAS." is a good book for begginer like me , so the book give one part of the code that is the union and said that i have to show the variables in the display serial and analyst the results , this is the code that i do:

void setup() {

Serial.begin(9600);
}
union {
  int i;
  char c;
  long u;
  float x;
  word w;
}comando;
void loop() {
comando.x=M_PI;// asignacion de una costante de tipo flotante (numero pi)
//bitSet(comando.x,16); // cambiar el bit 16 de x
Serial.print(F("Variable tipo char:  "));
Serial.println(comando.c);
Serial.print(F("Variable tipo int:  "));
Serial.println(comando.i);
Serial.print(F("Variable tipo long:  "));
Serial.println(comando.u);
Serial.print(F("Variable tipo float:   "));
Serial.println(comando.x);
Serial.print(F("Variable tipo word :   "));
Serial.println(comando.w);
Serial.print(F("Se repitira en 10 segundos"));
delay(10000);
}

In screen show :

Variable tipo char:  ⸮
Variable tipo int:  4059
Variable tipo long:  1078530011
Variable tipo float:   3.14
Variable tipo word :   4059
Se repitira en 10 segundos

So i dont understand the results because i give x the value of the number pi so what i understand is that union make that all the variables modify with this value so why i is not 3? that is the whole part of 3.1416, the same for w, u i dont understand why is so big and in w and i is so small, c i believe that because it is a fraction and only number int can pass to letters or other numbres , if someone can explain me this i will be very gratefull.

The second question is why can not configure the bits of x? i try to change the bit 16 of x but this said that in arduino one cant do this, but i read that arduino one can use bitSet so i dont undestand why this dont let me use bitSet, i put this part like comment to make tests , thank you for everything that you will say me and if i found how to solve this questions i will post here the solution for people that in the future need this.

Sorry for my english, i am good to read but bad to write, in the future i will try to make my english more smooth

CambioDeTipoPro.ino (655 Bytes)

3

Ohhh are the bytes shared and no the value , thank you , i use this page Online Binary-Decimal Converter to calculate the bytes , and now all have sense.
Now my only question is why i cant modificate the bits of x? with //bitSet(comando.x,16); // cambiar el bit 16 de x , every time that i uncomment
this part said "exit status 1
Error compilando para la tarjeta Arduino/Genuino Uno." i dont know why

4 
/Users/john/Documents/Arduino/sketch_dec10a/sketch_dec10a.ino: In function 'void loop()':
/Users/john/Library/Arduino15/packages/arduino/hardware/avr/1.6.20/cores/arduino/Arduino.h:112:37: error: invalid operands of types 'float' and 'long unsigned int' to binary 'operator|'
 #define bitSet(value, bit) ((value) |= (1UL << (bit)))
                                     ^
/Users/john/Documents/Arduino/sketch_dec10a/sketch_dec10a.ino:15:3: note: in expansion of macro 'bitSet'
   bitSet(comando.x,16); // cambiar el bit 16 de x
   ^

It's saying that you can't set bits in a float (it's an invalid type on the left side of the |= operator). If you want to set Bit 16, set it in comando.u. Since the two variable are sharing memory it will set Bit 16 in comando.x. Don't use comando.i, comando.c, or comando.w since none of them have a Bit 16.

6

thank you for everything , now i know that union share the bits so if i change the bite 31 change the sign of the variable long and float , also that bitSet cant change variables float.