LAB 03 QUESTIONS SOLUTION

Answer the questions below according to the lab specification. Write
your answers directly in this text file and submit it to complete the
lab.


PROBLEM 1: Number conversions
=============================

A
~

  Fill in the following table of equivalences.  Filling in the table
  from top to bottom is advantageous as earlier rows can sometimes be
  used to infer lower values. Feel free to make use of any ASCII table
  or the table.c program provided in the week 3 lecture code pack.

   Dec   Hex  Oct  Binary     Char         
  -----------------------------------------
     9  0x09   11  0000 1001  TAB          
    10                        \n (newline) 
        0x20                  SPACE        
                   0011 0010               
    65  0x41  101  0100 0001  A            
    66                                     
        0x4F  117             O            
    80                        P            
    91        133  0101 1011  [            
    97  0x61  141                          
              172  0111 1010  z            
   145  0x91  221             none         
   160             1010 0000  none         
   180  0xB4  264             none         
   255                        none         


B
~

  Fill in the bits, hex, and decimal values for the given examples. The
  first example is completed for you. Assume all of these are 32 bit
  unsigned integers.
  ,----
  |   COMPLETED
  |   Binary:   0000 0000  0000 0000  0001 1000  1110 1001  
  |             0    0     0    0     1    8     E    9
  |   Hex   :   0018E9
  |   Decimal:  6377
  | 
  | 
  |   NUMBER 1
  |   Binary:   0000 0000  0010 1111  0011 1010  1000 1101  
  |             ?
  |   Hex   :   ??
  |   Decimal:  ??
  | 
  | 
  |   NUMBER 2
  |   Binary:   ??  
  |             7    F     8    3     5    A     0    B
  |   Hex   :   7F835A0B
  |   Decimal:  ??
  `----


PROBLEM 2: Signed Integer Conversions
=====================================

A
~

  Apply the steps involved in converting the following positive binary
  number to it's two's complement negation in 8-bit signed
  format. Recall the steps are
  - Subtract 1
  - Invert the bits
  ,----
  | 0111 1100  = 0x7C = 124 (decimal)
  `----
  The result is the two's complement representation of -124.

  Reverse the process by
  - Invert the bits
  - Add one
  to show that the original bits are gotten back.


B
~

  Complete the following table of equivalences assuming 8-bit
  twos-complement signed integers. The rightmost column is the inverse
  of the binary representation: flip 1's to 0's, and vice versa.

    Dec   Hex  Binary     Inverse   
  ----------------------------------
     +5  0x05  0000 0101  1111 1010 
     -5        1111 1011            
    +32  0x20                       
    -32  0xE0             0001 1111 
   +127  0x7F                       
   -127  0x81                       
   -128        1000 0000            
     +2                             
     -2  0xFE                       
     +1  0x01  0000 0001            
     -1        1111 1111            
      0                             


PROBLEM 3: Converting Strings to Numbers
========================================

  Inspect the program in the lab pack called `convert.c'.  Compile and
  run it using
  ,----
  | > gcc convert.c
  | > ./a.out
  `----
  Describe briefly what kind of conversion is being done by the
  `convert()' function given.
  - A. What kind of data is input?
  - B. What result is produced by the function?
  - C. How is a success versus an error reported?
  - D. Why is this kind of conversion needed?
  - E. What built-in C function (useful for the assignment) does this
    conversion function use and how is its calling convention different
    from convert()?