Trying to copy elements from one array to another using only pointers - c++

Question

My professor wants me to only use pointers, no subscripts are permitted in any function
I'm suppose to let the user input two size and elements into two separate arrays and then make a union function which finds all elements that are the same (no duplicate values in either array)
All I want to do is move my array elements from the first array to the union array but I just get random numbers when I execute the program
void get_union(short *set1,short size1,short *set2,short size2,short *union_array,short size_union) // look at call statement to assist incompleting this statement
{
short *end1=(set1+size1), //*end2=(set1+size1+size2);
for( ;set1<end1;set1++)
{
union_array=set1;
cout<<"Union array value number "<<count++<<" "<<*union_array++<<endl;
}
}
and also I tried memcpy but I have never used it before especially not with pointers
memcpy(union_array,set1,sizeof(union_array));
Here's my first two functions that lets the user input data, and then displays it.
void inputData(short *data, short size) // function to enter data into the array
{
short count=1;
short *end=(data+size);
for( ;data<end;data++)
{
cout<<"Enter Number "<<count++<<" : ";
cin>>*data;
cout<<endl;
}
}
and
void displayData(short *data, short size) // function to display data in an array
{
short count;
short *end=(data+size);
for( ;data<end;data++)
{
cout<<"Number "<<count++<<" : "<<*data<<endl;
}
}
This is what I get when I run the program. The whole thing runs through but the union array gets random numbers
enter the number of values to store in the data set 1
or zero to terminate the program
3
Enter Number 1 : 2
Enter Number 2 : 4
Enter Number 3 : 6
there are 3 values in the array set1
Number 0 : 2
Number 1 : 4
Number 2 : 6
enter the number of values to store in the data set 2
3
Enter Number 1 : 10
Enter Number 2 : 11
Enter Number 3 : 12
there are 3 values in the array set2
Number 0 : 10
Number 1 : 11
Number 2 : 12
Union array value number 1 -5245
the union array contains 0 values
the intersection array contains -1 values

Answer 1

I'm not sure about your question, but let me try to help you:
All I want to do is move my array elements from the first array to the union array but I just get random numbers when I execute the program
using namespace std;
void get_union(short *set1,short size1,short *union_array,short size_union) {
for (; size1; --size1) {
*union_array++ = *set1++;
}
}
int main () {
short set1[] = {1, 0, 15, 35, 200, 12};
size_t size = sizeof(set1) / sizeof(*set1);
short union_arr[size];
get_union(set1, size, union_arr, size);
for (size_t i = 0; i < size; i++) {
cout << union_arr[i] << " ";
}
cout << endl;
return 0;
}
make a union function which finds all elements that are the same (no duplicate values in either array)
size_t get_union(short *set1, unsigned size1, short *set2, unsigned size2, short *union_array, unsigned size_union) {
size_t count = 0;
// TODO:: Make sure that the arrays are already sort
// todo:: or use the following two commands:
qsort(set1, size1, sizeof(*set1), [](const void * a, const void * b) -> int{
return ( *(short*)a - *(short*)b );
});
qsort(set2, size2, sizeof(*set2), [](const void * a, const void * b) -> int{
return ( *(short*)a - *(short*)b );
});
while (size1 && size2) {
if (*set1 > *set2) {
++set2;
--size2;
} else if (*set1 < *set2) {
++set1;
--size1;
} else {
*union_array++ = *set1++;
--size1;
++set2;
--size2;
++count;
}
}
return count;
}
int main () {
short set1[] = {1, 0, 15, 35, 200, 12};
short set2[] = {50, 0, 15, 0, 200, 12};
size_t size = sizeof(set1) / sizeof(*set1);
short union_arr[size];
size_t count;
count = get_union(set1, size, set2, size, union_arr, size);
cout << count << endl;
for (size_t i = 0; i < count; i++) {
cout << union_arr[i] << " ";
}
cout << endl;
return 0;
}
Btw, it is C question more then C++ one.. In C++ you can simply use vectors, and make the code as simple as you can (and the union array will be axactly with the minimum size). Pointers in C++ are more relevant in different situations, when you dealing with speed situations and APIs..

Answer 2

What he wants from us it to write a function that compares two arrays (set1 and set2 that I had) and puts all numbers that occur in either. so if there are 0 elements in the first array and 5 in the other, then the union array should have 5 elements
size_t get_unique_union(short *arr, size_t size, short *target) {
size_t target_bigger = 0;
short *curr, *curr_test;
//size_t dup = 0; (1)
if (!size) {
return target_bigger;
}
curr = arr + 1; // Current place in the array.
curr_test = curr; // Current place with the offset of the duplicate elements.
while (curr_test < arr + size) {
while (curr_test < arr + size && *arr == *curr_test) {
curr_test++;
//dup++; // | (1) Update global size. see comment.
}
*curr++ = *curr_test++;
}
size -= curr_test - curr; // Update global size | (1) size -= dup;
if (curr == curr_test) { // If it is a unique appearance (If there were no founded duplicates).
*target = *arr; // Set target in the current place the appearance.
target_bigger = 1; // Mention that in the next recursive calling,
// it will be called from the next place in the unique array.
}
for (size_t i = 0; i < size; i++) { // Display the current checked array (Without the doubles of the current appearance).
cout << arr[i] << " ";
}
cout << endl;
return target_bigger + get_unique_union(arr + 1, size - 1, target + target_bigger); // Recursive call with the next element in the array.
}
size_t get_union(short *set1, unsigned size1, short *set2, unsigned size2, short *uniq_arr) {
size_t global_size = size1 + size2;
size_t uniq_size = 0;
short union_array[global_size];
for (size_t i = 0; i < size1; i++) {
union_array[i] = set1[i];
}
for (size_t i = 0; i < size2; i++) {
union_array[i + size1] = set2[i];
}
for (size_t i = 0; i < global_size; i++) {
cout << union_array[i] << " ";
}
cout << endl;
return get_unique_union(union_array, global_size, uniq_arr);
}
int main () {
short set1[] = {12, 0, 2, 1, 12, 12, 6, 8};
short set2[] = {3, 0, 300, 12, 12, 12};
size_t size1 = sizeof(set1) / sizeof(*set1);
size_t size2 = sizeof(set2) / sizeof(*set2);
short union_arr[size1 + size2];
size_t count;
count = get_union(set1, size1, set2, size2, union_arr);
cout << "Results:" << endl;
cout << "Count: " << count << endl;
cout << "Arr: [";
for (size_t i = 0; i < count; i++) {
cout << union_arr[i] << ((i < count - 1) ? ", " : "");
}
cout << "]" << endl;
return 0;
}
This code even take care of cases that there are duplicates in the same array. It combines the arrays to the same big array, remove duplicates, and insert only the elements that have no duplicates at all.
Pay attention that the function "get_unique_union" is recursive, and returns the count of the unique elements, and not the unique union array's real size.
The code format is C one, and not C++ (it works on C++, has been written in cpp file and compiled with g++ compiler. But in C++ it would be write with vectors, and it would save more useless place in the unique union array).