# Doubt in negative numbers in binary format

Deepika Namasani

Greenhorn

Posts: 25

posted 11 years ago

public class test33

{

public static void main(String args[])

{

int i = -1;

i = i >> 1;

System.out.println(i);

}

}

answer for this code is -1

since it is -1 something like this

since i is int it is 32 bit(4 byte)

10000000 00000000 00000000 00000001

but when it is >>1(signed right shift it is )

11000000 00000000 00000000 00000000

so how did -1 come

pls clarify this one

thanks

{

public static void main(String args[])

{

int i = -1;

i = i >> 1;

System.out.println(i);

}

}

answer for this code is -1

since it is -1 something like this

since i is int it is 32 bit(4 byte)

10000000 00000000 00000000 00000001

but when it is >>1(signed right shift it is )

11000000 00000000 00000000 00000000

so how did -1 come

pls clarify this one

thanks

Deepika N

posted 11 years ago

-1 = 11111111 11111111 11111111 11111111

Java like many other languages/processors uses two's complement. To negate a number you need to complement the number and add one.

Henry

[ May 24, 2005: Message edited by: Henry Wong ]

since it is -1 something like this

since i is int it is 32 bit(4 byte)

10000000 00000000 00000000 00000001

-1 = 11111111 11111111 11111111 11111111

Java like many other languages/processors uses two's complement. To negate a number you need to complement the number and add one.

Henry

[ May 24, 2005: Message edited by: Henry Wong ]

posted 11 years ago

this last line is incorrect. to get the binary representation of a number, follow these steps:

write the positive number in binary. so for -1, we'd write 1 in binary:

00000000 00000000 00000000 00000001

now, flip every bit to it's alternate state:

11111111 11111111 11111111 11111110

Last, add 1:

11111111 11111111 11111111 11111111

now that we have -1 in binary, we can do the bit shift. move everything over one bit, keep the sign bit, and we get:

11111111 11111111 11111111 11111111

which is -1.

[ May 25, 2005: Message edited by: fred rosenberger ]

since it is -1 something like this

since i is int it is 32 bit(4 byte)

10000000 00000000 00000000 00000001

this last line is incorrect. to get the binary representation of a number, follow these steps:

write the positive number in binary. so for -1, we'd write 1 in binary:

00000000 00000000 00000000 00000001

now, flip every bit to it's alternate state:

11111111 11111111 11111111 11111110

Last, add 1:

11111111 11111111 11111111 11111111

now that we have -1 in binary, we can do the bit shift. move everything over one bit, keep the sign bit, and we get:

11111111 11111111 11111111 11111111

which is -1.

[ May 25, 2005: Message edited by: fred rosenberger ]

There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors

amit taneja

Ranch Hand

Posts: 813

posted 11 years ago

ok lowercase DAd...

but can u pls tell me that why we do

two complement for getting nagative...

why don't

-1 is like 10000000 00000000 00000000 00000001

as we have negative signbit (1 on leftmost) and rest of the no.

then why we complement the bits and add one

i think we add one becasue negative value has one no. more capacity w.r.t positive no.

but why complements ?

plss explain.

but can u pls tell me that why we do

two complement for getting nagative...

why don't

-1 is like 10000000 00000000 00000000 00000001

as we have negative signbit (1 on leftmost) and rest of the no.

then why we complement the bits and add one

i think we add one becasue negative value has one no. more capacity w.r.t positive no.

but why complements ?

plss explain.

Thanks and Regards, Amit Taneja

posted 11 years ago

The main reason for using twos complement to represent negative numbers is to make it easy to add (and subtract) two signed numbers. Adding 17 and -4 looks like this in binary (showing only 8 bits to keep it short):

0001 0001 (17)

+ 1111 1100 (-4)

= 0000 1101 (13)

It is more expensive to basic arithmetic without using twos complement.

The reason there is one more negative value to a signed integer type is because we use twos complement, not the other way around.

0001 0001 (17)

+ 1111 1100 (-4)

= 0000 1101 (13)

It is more expensive to basic arithmetic without using twos complement.

The reason there is one more negative value to a signed integer type is because we use twos complement, not the other way around.

SCJP, SCWCD