十进制到二进制格式的转换

Question

I have to write a Java program as part of an assignment to convert decimal inputs to the following formats: unsigned binary, unsigned hex, signed-magnitude, 1's complement and 2's complement . The issue is that I am not allowed to use any of the built-in java components that would otherwise not make this so difficult. I've been working on this for a number of hours, and the last thing I wanted to do was come on here and ask for help, but I really am stumped here. I do not expect, nor am I looking for anyone to complete my homework for me. All I ask is for a nudge in the right direction.

The output/input of the program must be as follows:

Enter num bytes: 2

Enter number (or Q to quit): 4095

Input number=4095
    Unsigned binary = 0000 1111 1111 1111   (0x0fff)
    Signed-magnitude = 0000 1111 1111 1111
    One's complement = 0000 1111 1111 1111
    Two's complement = 0000 1111 1111 1111
    Excess 32768 = 1000 1111 1111 1111

Enter number (or Q to quit): -4095

Input number=-4095
    Unsigned binary = undefined
    Signed-magnitude = 1000 1111 1111 1111
    One's complement = 1111 0000 0000 0000
    Two's complement = 1111 0000 0000 0001
    Excess 32768 = 0111 0000 0000 0001

I have a good understanding of how to calculate these values, and I have worked out many of the algorithms accordingly. The issue I'm having is that I don't know how to properly organize my classes to make this program efficient. Mostly, I'm getting confused by the instructions I've been given.

They read as follows:

Don't use the byte data type in Java. We want to show the algorithms we use to do binary encodings. I created a simplistic BitString class. It's one field is an array of char's. It has methods like: BitString( numBytes), clear(), invert(), encodeUnsigned( num), setBit( pos, char).

I don't understand why we would want to use a char array to store these bit values. I've set this up so that the constructor in BitString accepts an argument for the number of bytes, multiplies that by 8 and creates a new char array using this number. Then to obtain the unsigned binary value of the decimal, I've implemented the following:

String unsigned = "";
while(decimal > 0)
{
  unsigned = decimal%2 + unsigned;
  decimal = decimal >> 1;
}

I don't know what I'm supposed to do from here to be able to store these values in that array so that I can use it to calculate the other formats. I can't seem to be able to store integers as chars and I'm confused on how I am supposed to use that data structure to perform the other operations. To complicate matters further, you'll notice that I need to pad the data so that it contains the correct number of bits.

If this were your problem, how would you solve it and how would you lay it out? I'm looking for the most fundamental solution that would be easy for a novice like me to understand. Thank you very much.

Answer 1

The instructions probably mean that, instead of

String unsigned = "";

The data would be more easily manipulated into other formats with something like (this is pseudo-code, I don't really know java):

char unsigned[numBytes * 8];

The array stores one bit per location.

To do bitwise operations, you just iterate through the array and operate on each "bit."