# demonstrate how to convert step by step 130 to fit in a byte variable

pedro abs

Ranch Hand

Posts: 33

posted 6 years ago

someone, please, can demonstrate how the cast is made of the number 130 to fit into a variable of type byte? Step by step ....

I try begin doing this:

130 / 2 = 65

Mod 0

65 / 2 = 32

Mod 1

32 / 2 = 16

Mod 0

16 / 2 = 8

Mod 0

8 / 2 = 4

Mod 0

4 / 2 = 2

Mod 0

2 / 2 = 1

Mod 0

1 / 2 = 0

Mod 1

then 130 = 1000 0010

then....???

I try begin doing this:

130 / 2 = 65

Mod 0

65 / 2 = 32

Mod 1

32 / 2 = 16

Mod 0

16 / 2 = 8

Mod 0

8 / 2 = 4

Mod 0

4 / 2 = 2

Mod 0

2 / 2 = 1

Mod 0

1 / 2 = 0

Mod 1

then 130 = 1000 0010

then....???

posted 6 years ago

Welcome to JavaRanch.

I'm not sure exactly what you want to know. The value 130 does not fit into a byte, because a byte is an 8-bit signed data type - it can contain only values between -128 and 127. Values in a byte (as well as in int, short and long) are stored in two's complement format.

I'm not sure exactly what you want to know. The value 130 does not fit into a byte, because a byte is an 8-bit signed data type - it can contain only values between -128 and 127. Values in a byte (as well as in int, short and long) are stored in two's complement format.

posted 6 years ago

It is possible to use a byte to store that bit pattern, but Java will interpret it as a signed two's complement integer, and you'll end up with a negative value: -126.

However, if you

All you need is to widen from a byte to an int and do some bit twiddeling:

I guess the real question is, why would you want to do this?

However, if you

*know*the byte's bit pattern should be interpreted as an unsigned value, you can work around this.All you need is to widen from a byte to an int and do some bit twiddeling:

I guess the real question is, why would you want to do this?

Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.

Nicola Garofalo

Ranch Hand

Posts: 308

posted 6 years ago

As you wrote 130 in binary representation is

the leftmost bit is set to 1, so the number will be negative

now flip all the bits

add

in decimal is 126 but remember that the leftmost bit was 1 then the number is negative

=

**1 0 0 0 0 0 1 0**the leftmost bit is set to 1, so the number will be negative

now flip all the bits

**0 1 1 1 1 1 0 1**add

**1****0 1 1 1 1 1 1 0**in decimal is 126 but remember that the leftmost bit was 1 then the number is negative

=

**- 126**Bye,

Nicola

pedro abs

Ranch Hand

Posts: 33

posted 6 years ago

That's what I want to understand.

(why casting 130 to byte results -126)

But why I have to flip all the bits and then add 1?

how this algorithm?

Thanks everybody !!!

Nicola Garofalo wrote:As you wrote 130 in binary representation is

1 0 0 0 0 0 1 0

the leftmost bit is set to 1, so the number will be negative

now flip all the bits

0 1 1 1 1 1 0 1

add1

0 1 1 1 1 1 1 0

in decimal is 126 but remember that the leftmost bit was 1 then the number is negative

=- 126

That's what I want to understand.

(why casting 130 to byte results -126)

But why I have to flip all the bits and then add 1?

how this algorithm?

Thanks everybody !!!

Nicola Garofalo

Ranch Hand

Posts: 308

posted 6 years ago

That's the two's complement system.

Follow the link that Jesper Young posted in one of the previous messages

I think there you will find all you need to know about it.

http://en.wikipedia.org/wiki/Two's_complement

Follow the link that Jesper Young posted in one of the previous messages

I think there you will find all you need to know about it.

http://en.wikipedia.org/wiki/Two's_complement

Bye,

Nicola