// copy all of the values in source1 which are also found in source2 into destination
// return the number of elements copied into destination

int common_elements(int length, int source1[length], int source2[length], int destination[length]) {
    // PUT YOUR CODE HERE (you must change the next line!)
    return 42;
}

// You may optionally add a main function to test your common_elements function.
// It will not be marked.
// Only your common_elements function will be marked.