MCX1/4                                                                                                             Math Department
Mr. Gary. Jaye                                                                                                    Danny Jaye, A.P.S.

1998 Question 1 from APCS A Exam: Part II

Assume that registration codes, each consisting of a sequence of characters, are implemented using the constants
and class declaration below.

const int MINLEN = 5;
const int MAXLEN = 15;

class Code
{
    public:
      Code();                   // length is 0, capacity is MAXLEN chars
      Code(const apstring & s); // code has chars in s, length is s.length()
      bool IsValid();           // returns true if code is valid, else false
      int  Length();            // returns # characters in the code
      void AppendCheckSum();    // adds appropriate check sum to the code

      // other member functions not shown

    private:
      int myLength;            // # characters in code
      apvector<char> myChars;  // the characters in the code
};

Part A
Write the member function IsValid, whose header is given below. IsValid returns true if a code is valid and 
returns false otherwise. A code is valid if it satisfies the following criteria. 

1. The length is greater than or equal to MINLEN and less than or equal to MAXLEN - 2,
   i.e., MINLEN <= Length() <= MAXLEN - 2
2. Each character is either a digit ('0'..'9') or a capital letter ('A'..'Z').

For example, consider the values of a Code variable c shown below.

In writing IsValid you may call the functions isdigit and isupper whose headers are shown below. You do
not need to write isdigit or isupper.

bool isdigit(char ch)
// postcondition: returns true if and only if ch
//                       is a digit: '0' .. '9'

bool isupper(char ch)
// postcondition: returns true if and only if ch
//                      is an upper case letter: 'A' .. 'Z'

Complete member function IsValid below.

bool Code::IsValid()
// postcondition: returns true if MINLEN <= Length() < MAXLEN - 2
//                and for every k, 0 <= k < Length(),
//                myChars[k] is a digit '0'--'9' or a char 'A' -- 'Z'
 
 

Part B

Consider the problem of appending a checksum to the end of a registration code. The checksum is computed as follows:

• For each character in the registration code that is a digit, add the corresponding integer value to a running total.
• The checksum is the rightmost digit of the total.

Write the member function AppendCheckSum, whose header is given below. If a Code value is valid as specified
in part (a), then AppendCheckSum should calculate the checksum and append the character '-' followed by the
character for the checksum to the original Code value; otherwise AppendCheckSum should leave the original Code
value unchanged.

For example, if c is a variable of type Code

The functions digitToInt and intToDigit convert from a digit character to the equivalent integer and
from a  one-digit integer to the equivalent character, respectively.

int digitToInt(char d) {
// precondition:  isdigit(d) == true
// postcondition: returns the value 0 to 9 corresponding
//                to character d


char intToDigit(int val) {
// precondition: 0 <= val <= 9
// postcondition: returns the character from
//               '0'..'9' corresponding to val


In writing AppendCheckSum, you may call the functions intToDigit, digitToInt, isupper and 
isdigit specified above and in part (a) (you do not have to write the bodies of these functions.)
You may also call member function IsValid specified in part (a). Assume that IsValid 
works as specified, regardless of what you wrote in part (a).

Complete member function AppendCheckSum below.

void Code::AppendCheckSum() {
// postcondition:  if IsValid() then myLength is updated and
//                        myChars contains the original characters followed
//                        by a dash and the appropriate checksum; otherwise
//                       myLength and myChars are unchanged
   

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