CSE 109 Test 2  20 November 2002
>>>>>>>>>>>>>>SUGGESTED ANSWERS<<<<<<<<<<<<<<<<<<<<<<<<<
1.  Given the class A below, write the declaration and definition (code) for
B, a subclass of A so that the code below the first dashed line produces all
four characters of the output below the second dashed line.
  class A
  {public:
    A(int x=0);
    int get(); //returns the value of data
   private:
    int data;
  };
---------------------------------------------------
 B a(20);
 a.display();
---------------------------------------------------
 [20]
=====================================================
class B : public A
{public:
  B(int x=0);
  void display();
};

 B::B(int x):A(x){}
 void B::display(){cout<<'['<<get()<<']';}

2.  Assume you have a class HashTable of fixed size 2003 (which is prime),
implemented with the data member   int table[2003]; The table is meant
to store social security numbers and is initialized with 0's.  Write the
prototype and definition of the HashTable member function "location" which
returns -1 if some entry is not in the table and returns the index of an entry
if the entry is in the table.  "location" should assume that the number itself
is used for the hash number and that a quadratic probe is used to store
entries.  If ht is of type HashTable, the call to location() might be
int x=ht.location(30204055);
===============================================
int HashTable::location(int x)
{int hash,j,loc;
 if(x<0)
   return -1;
 hash=x%2003;
 j=0;
 while(j<2003/2)
 {loc=(hash+j*j)%2003;
  if(tab[loc]==0)
    return -1;
  if(tab[loc]==x)
    return loc;
  j++;
 }
 return -1;
}

3.  Write a function "equal" which is free of bugs, e.g., segmentation faults,
and determines whether the first n characters of two strings are identical.
Given the declarations
  char *a,*b;
  int n;
the call to "equal" would look like
  if(equal(a,b,n))
    cout<<"EQUAL";
===========================================================
bool equal(char *a, char*b,int n)
{int loc;
 if(a==NULL || b==NULL)
   return a==b;
 if(n<=0)
   return true;
 loc=0;
 while(loc<n && a[loc]==b[loc] && a[loc]!='\0')
   loc++;
 return a[loc]==b[loc] || loc==n;
}

4.  Write the OP2 code which corresponds to the following ASM2F program.
Recall the OP2 codes:  read(0), write(1), load immediate(2), store(3),
add(4), subtract(5), multiply(6), divide(7), jump(8), compare and jump(9).
      JMP PROG
 SUM: VAR
 MAX: CNST 100
 PROG:
      LDI 0
      STO SUM
 LOOP:
      RD
      SUB ACCUM,MAX
      CJP MORE,ACCUM
 MORE: ADD ACCUM,MAX
       ADD ACCUM,SUM
       STO SUM
       JMP LOOP
 END
 8 9 90 905
===========================
8004000
0
100
2000000
3002000
0
5000003
9009000
4000003
4000002
3002000
8006000
E
8 9 90 905