Question

I have an assignment where I have to create 3 arrays. The first two arrays have similar elements and the third is empty.

const int arraySize = 4;
array k[arraySize] = {1, 2 ,3, 7}
array j[arraySize] = { 1, 2, 8, 9}
array u;

int *ptr1 = arrayk;
    int *ptr2 = arrayj;

How could I compare the elements in the first two and then copy over those duplicates to the third empty array (array u)?

I was thinking something like this:

for(int i = 0; i < arraySize; ++1) {
    for(int k = 0; k < arraySize; ++k) {
        if(&ptr1[i] == &ptr2[k]) {
            //copy elements that are duplicates to array u
          }
      }
}

Answer 1

Since it looks like homework, I’m assuming you want to do it by yourself not by using a library to achive this. This being the case, your code is fine, you just have to keep an integer variable to store the next available position in u array.

const int arraySize = 4; 
int next = 0; 
array k[arraySize] = {1, 2 ,3, 7};
array j[arraySize] = { 1, 2, 8, 9};
array u[arraySize]; // Because it at most be a copy of array k or j

for(int i = 0; i < arraySize; ++i) {
    for(int k = 0; k < arraySize; ++k) {
        if(arrayk[i] == arrayj[k]) {
            u[next++] = arrayk[i];
        }
    }
}

This way, when you find a duplicate you assign it to the next available position on u and then increase the value of next by one.

Here is the pointer version, although I strongly recommend to avoid them in cases like this, and use them only when they are needed.

const int arraySize = 4; 
int next = 0; 
array k[arraySize] = {1, 2 ,3, 7};
array j[arraySize] = { 1, 2, 8, 9};
array u[arraySize]; // Because it at most be a copy of array k or j

int *ptr1 = arrayk;
int *ptr2 = arrayj;

for(int i = 0; i < arraySize; ++i) {
    for(int k = 0; k < arraySize; ++k) {
        if(*(ptr1 + i)  == *(ptr2 + k) {
            u[next++] = *(ptr1 + i);
        }
    }
}