#include <iostream>
#include <cctype>

using namespace std;

/**
 * Returns a ptr to the first instance of an element x in an arr arr of length n.
 * If not found, return NULL;
 */
int* find(const int arr[], int n, int x);

/**
 * Prints out array arr of length n.
 */
void printArray(const int arr[], int n);


int main()
{
  const int ARRAY_SIZE = 9;
  int x[ARRAY_SIZE] = {1, 2, 3, 4, 5, 4, 3, 2, 1};
  
  {
	int *ptr = find(x,ARRAY_SIZE,3);

	if (ptr != NULL) {
	  *ptr = 10;
	  cout << "Replaced 3 with 10: ";
	  printArray(x,ARRAY_SIZE);
	  cout << endl;
	}else {
	  cout << 3 << " not found" << endl;
	}
	
	
  }

  {
	int *ptr = find(x,ARRAY_SIZE,3);

	if (ptr != NULL) {
	  *ptr = 100;
	  cout << "Replaced 3 with 100: ";
	  printArray(x,ARRAY_SIZE);
	  cout << endl;
	} else {
	  cout << 3 << " not found" << endl;
	}
	
	
  }

  {
	int *ptr = find(x,ARRAY_SIZE,3);

	if (ptr != NULL) {
	  *ptr = 1000;
	  cout << "Replaced 3 with 1000: ";
	  printArray(x,ARRAY_SIZE);
	  cout << endl;
	} else {
	  cout << 3 << " not found" << endl;
	}
	
  }

}

void printArray(const int arr[], int n)
{
  cout << "{ ";
  for (int i=0;i<n;i++) {
	cout << arr[i] << " ";
  }
  cout << "}";
}

int* find(const int arr[], int n, int x)
{
  for (int i=0;i<n;i++) {
	if (arr[i] == x) {
	  return (int*) arr+i;

	  // Could also return &arr[i]
	}
  }
  
  return NULL;
}