Error : Display duplicated results via pointer - c++

Question

Goal state: I'm supposed to display a result where by randomized e.g. Set S = {dog, cow, chicken...} where randomized size can be 1-12 and animals cannot be replicated so once there is cow, there cannot be another cow in Set S anymore.
Error: I've been displaying a correct randomized size of 1-12. However I have duplicated animals even though I tried to check whether the animal exist in set S before I insert it into Set S.
UPDATE: I couldnt get it to run after the various updates by stackoverflow peers.
Constraints: I have to use pointers to compare with pointers - dynamically.
"Important Note
All storages used for the arrays should be dynamically created; and delete them when
they are no longer needed.
When accessing an element of the array, you should access it via a pointer, i.e. by
dereferencing this pointer. Using the notation, for example set [k] or *(set + k)
accessing to the kth element of the set is not allowed."
Do hope to hear your advice, pals!
Best regards,
MM
/*
MarcusMoo_A2.cpp by Marcus Moo
Full Time Student
I did not pass my assignment to anyone in the class or copy anyone’s work;
and I'm willing to accept whatever penalty given to you and
also to all the related parties involved
*/
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <ctime>
using namespace std;
/* Global Declaration */
const int MAX = 12; // 12 animals
const int MAXSTR = 10;
typedef char * Element;
static Element UniversalSet [MAX] = {"Rat", "Ox", "Tiger", "Rabbit", "Dragon",
"Snake", "Horse", "Sheep", "Monkey", "Rooster", "Dog", "Pig"};
/* Functions */
// Construct a set
void option0(int); // Menu Option 0
void constructSet (Element *, int); // Construct a set
bool checkElement (Element *, Element *, int); // Check element for replicates
int main()
{
// Declarations
int mainSelect;
int size=rand()%12+1; // Random construct
srand (time(NULL)); // Even better randomization
cout << "Welcome to MARCUS MOO Learning Center" << endl;
do
{
cout << "0. An example of set" << endl;
cout << "1. Union" << endl;
cout << "2. Intersection" << endl;
cout << "3. Complement" << endl;
cout << "4. Subset of" << endl;
cout << "5. Equality" << endl;
cout << "6. Difference " << endl;
cout << "7. Distributive Law" << endl;
cout << "9. Quit" << endl;
cout << endl;
if (mainSelect==0)
{
option0(size);
}
cout << "Your option: ";
cin >> mainSelect;
cout << endl;
} while(mainSelect!=9);
return 0;
}
/* Functions */
// Option 0 - An example of set
void option0 (int size)
{
// Mini Declaration
int again;
Element *S;
do
{
cout << "Here is an example on set of animals" << endl;
cout << endl;
// Build set S
constructSet (S,size);
// Display set S
Element *S = &S[0];
cout << "Set S = {";
for (int i = 0; i < size; i++)
{
if (i!=size)
{
cout << *S
<< ", ";
}
else
{
cout << *S
<< "}"
<< endl;
}
S++;
}
cout << endl;
cout << "Note that elements in S are distinct are not in order" << endl;
cout << endl;
// Option 0 2nd Part
cout << "Wish to try the following operations?" << endl;
cout << "1. Add an element to the set" << endl;
cout << "2. Check the element in the set" << endl;
cout << "3. Check the cardinality" << endl;
cout << "9. Quit" << endl;
cout << endl;
cout << "Your choice: ";
cin >> again;
} while (again!=9);
}
// Construct a set
void constructSet (Element *set, int size)
{
// Declarations
Element *ptrWalk;
ptrWalk = &set[0];
int randomA=0;
for (int i = 0;i<size;i++)
{
bool found = true;
while (found)
{
randomA = rand()%MAX; // avoid magic numbers in code...
*ptrWalk = UniversalSet [randomA];
// Ensure no replicated animals in set S
found = checkElement (ptrWalk, set, i);
}
set=ptrWalk;
set++;
}
}
bool checkElement (Element *ptrWalk, Element *set, int size)
{
for (int j=0; j<size;j++)
{
if (ptrWalk==&set[j])
{
return true;
}
}
return false;
}

Answer 1

You have 2 different major problems in your code. First has already be given by Federico: checkElement should return true as soon as one element was found. Code should become simply (but please notice the < in j<size):
bool checkElement (char *ptrWalk, int size)
{
for (int j=0; j<size;j++)
{
if (ptrWalk==S[j])
{
return true;
}
}
return false;
}
The second problem is that you should not search the whole array but only the part that has already been populated. That means that in constructSet you should call checkElement(ptrWalk, i) because the index of current element is the number of already populate items. So you have to replace twice the line
found = checkElement (*ptrWalk, size);
with this one
found = checkElement (*ptrWalk, i);
That should be enough for your program to give expected results. But if you want it to be nice, there are still some improvements:
you correctly declared int main() but forgot a return 0; at the end of main
you failed to forward declare the functions while you call them before their definition (should at least cause a warning...)
you make a heavy use of global variables which is not a good practice because it does not allow easy testing
your algorithms should be simplified to follow the Dont Repeat Yourself principle. Code duplication is bad for future maintenance because if forces to apply code changes in different places and omission to do so leads to nasty bugs (looks like this is bad but I've already fixed it - yes but only in one place...)
constructSet could simply be:
// Construct a set
void constructSet (Element *set, int size)
{
// Declarations
//Element *ptrBase;
voidPtr *ptrWalk;
ptrWalk = &set[0];
int randomA=0;
for (int i = 0;i<size;i++)
{
bool found = true;
while (found) {
randomA = rand()%MAX; // avoid magic numbers in code...
*ptrWalk = UniversalSet [randomA];
// Ensure no replicated animals in set S
found = checkElement (*ptrWalk, i);
}
ptrWalk++;
}
}

Answer 2

Main problem is that 'break' is missing in checkElement() once it finds the element. If you do not break the loop, it will compare with other indices and overwrite the 'found' flag.
if (ptrWalk==S[j])
{
found = true;
break;
}
Also, use ptrWalk as temporary variable to hold the string. Add the string to S only after you make sure that it is not present already.
void constructSet (Element *set, int size)
{
// Declarations
//Element *ptrBase;
Element ptrWalk;
//ptrWalk = &set[0];
int randomA=0;
int randomB=0;
bool found = false;
for (int i = 0;i<size;i++)
{
randomA = rand()%12;
ptrWalk = UniversalSet [randomA];
// Ensure no replicated animals in set S
found = checkElement (ptrWalk, i);
if (found==true)
{
do
{
// Define value for S
randomB = rand()%12;
ptrWalk = UniversalSet [randomB];
found = checkElement (ptrWalk, i);
} while(found==true);
S[i] = UniversalSet [randomB];
//ptrWalk++;
}
else
{
// Define value for S
S[i] = UniversalSet [randomA];
//ptrWalk++;
}
}
}
You need to optimize your code by removing unnecessary variables and making it less complex.

Answer 3

I have fixed this with the guidance of my C++ lecturer! You guys may take a reference from this to solve your pointers to pointers dilemma next time! Cheers!
/*
MarcusMoo_A2.cpp by Marcus Moo
Full Time Student
I did not pass my assignment to anyone in the class or copy anyone’s work;
and I'm willing to accept whatever penalty given to you and
also to all the related parties involved
*/
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <ctime>
using namespace std;
/* Global Declaration */
const int MAX = 12; // 12 animals
const int MAXSTR = 10;
typedef char * Element;
static Element UniversalSet [MAX] = {"Rat", "Ox", "Tiger", "Rabbit", "Dragon",
"Snake", "Horse", "Sheep", "Monkey", "Rooster", "Dog", "Pig"};
/* Functions */
// Construct a set
void option0(int); // Menu Option 0
void constructSet (Element *, int); // Construct a set
bool checkElement (Element, Element *, int); // Check element for replicates
// This function is to get a random element
// with storage allocated
Element getAnElement ()
{
Element *p = &UniversalSet [0];
int k = rand () % MAX;
for (int i = 0; i < k; i++)
++p;
Element e = new char [MAXSTR];
strcpy (e, *p);
return e;
}
int main()
{
// Declarations
int mainSelect;
int size=rand()%12; // Random construct
srand (time(NULL)); // Even better randomization
cout << "Welcome to MARCUS MOO Learning Center" << endl;
do
{
cout << "0. An example of set" << endl;
cout << "1. Union" << endl;
cout << "2. Intersection" << endl;
cout << "3. Complement" << endl;
cout << "4. Subset of" << endl;
cout << "5. Equality" << endl;
cout << "6. Difference " << endl;
cout << "7. Distributive Law" << endl;
cout << "9. Quit" << endl;
cout << endl;
if (mainSelect==0)
{
option0(size);
}
cout << "Your option: ";
cin >> mainSelect;
cout << endl;
} while(mainSelect!=9);
return 0;
}
/* Functions */
// Option 0 - An example of set
void option0 (int size)
{
// Mini Declaration
int again;
Element *S;
// You need to assign storage
S = new Element [MAX];
for (int i = 0; i < MAX; i++)
S [i] = new char [MAXSTR];
do
{
cout << "Here is an example on set of animals" << endl;
cout << endl;
// Build set S
constructSet (S,size);
// Display set S
Element *p = &S[0]; // Change to p
cout << "Set S = {";
for (int i = 0; i < size; i++)
{
if (i!=size-1)
{
cout << *p
<< ", ";
}
else
{
cout << *p
<< "}"
<< endl;
}
p++;
}
cout << endl;
cout << "Note that elements in S are distinct are not in order" << endl;
cout << endl;
// Option 0 2nd Part
cout << "Wish to try the following operations?" << endl;
cout << "1. Add an element to the set" << endl;
cout << "2. Check the element in the set" << endl;
cout << "3. Check the cardinality" << endl;
cout << "9. Quit" << endl;
cout << endl;
cout << "Your choice: ";
cin >> again;
} while (again!=9);
}
// Construct a set
void constructSet (Element *set, int size)
{
// Declarations
Element *ptrWalk;
ptrWalk = &set[0];
int randomA=0;
Element temp = new char [MAXSTR];
for (int i = 0;i<size;i++)
{
bool found = true;
while (found)
{
// randomA = rand()%MAX; ..
temp = getAnElement ();
// Ensure no replicated animals in set S
found = checkElement (temp, set, i);
}
// set=ptrWalk;
// set++;
strcpy (*ptrWalk, temp);
++ptrWalk;
}
}
bool checkElement (Element ptrWalk, Element *set, int size)
{
Element *p = &set[0];
for (int j=0; j<size;j++)
{
if (strcmp (ptrWalk, *p) == 0)
{
return true;
}
p++;
}
return false;
}