# How to Use Pointers

# Pointers to Arrays

When an array is created, the array name automatically contains the address of the first element in the array.
Since the array name contains an address, we can use this value to initialize a pointer.
We don't have to use the address of operator & in front of the variable name of array to get that address.
Althought an array name represents an address, it's technically not a pointer.
We can use the pointers to get all the values in an array using pointer arithmetic.

#include "stdafx.h"
#include <iostream>

using namespace std;

int main() {
  double values[10];        // declare an array values with 10 elements
  double* pValue = values;  // define a pointer to the array
  cout << "value array address: " << values << endl;
  cout << "pValues: " << pValue << endl;

  int numbers[10];
  int* pNumbers = numbers;
  for (int i = 0; i < 10; i++) {
    cout << "Numbers address " << i << ": " << pNumbers + i << endl;
  }

  return 0;
}

# Character Pointers

The character pointer is used to point to a string literal, since strings are really a sequence of individual characters.
When we try to print the address using a character pointer, we'll probably get some unprintable characters.
If we want to get the address of a single character, we actually have to use what's called casting.
We use single quotes ' around the P that indicates a character rathern than a string.
When the character pointer is used to point to the start of a string literal, it assigns the starting address as the first character in that string literal which is an array.
Since strings are immutable, it's a good programming practice to create the pointer as a constant pointer using the key word constant.
By assigning the pointer as a constant, it syncs the constant string literal with the constant pointer.
To output a string defined using a character pointer, simply use the pointer name. We don't need to use the dereference symbol *.

#include "stdafx.h"
#include <iostream>

using namespace std;

int main() {
  // Character Pointer and Casting
  char initial = 'P';
  char* pInitial = &initial;
  cout << "Memory address for initial P: " << pInitial << endl;
  cout << "Memory address for initial P: " << (void *) pInitial << endl;              // Casting Method 1
  cout << "Memory address for initial P: " << static_cast <void *>(pInitial) << endl; // Casting Method 2

  // Create the Character Pointer as a Constant Pointer
  const char* pans1{ "Absolutely Yes" };
  const char* pans2{ "Absolutely Yes" };
  const char* pans3{ "Absolutely Yes" };
  const char* pans4{ "Absolutely Yes" };
  const char* pans5{ "Absolutely Yes" };
  const char* pans6{ "Absolutely Yes" };
  const char* pans7{ "Absolutely Yes" };
  const char* pans8{ "Absolutely Yes" };
  const char* pans{ "Absolutely Yes" };
  int choices{};
}

# Dereferencing the Pointers

When we use the asterisk symbol * prior to the pointer name, it allows us access to the contents of the memory location to which it points.
The asterisk symble prior to the pointer name is so-called Deference Pointer or Indirection Pointer.
The deference pointer can be used with any of our numeric pointers excepts the character pointer.
When we're using a character pointer, we have to actually cast the value if we want to get at the data.

#include "stdafx.h"
#include <iostream>

using namespace std;

int main() {
  double testScores[5], sum = 0;
  double* pTestScores;
  pTestScores = testScores;

  for (int i = 0; i < 5; i++) {
    cout << "Enter the test score: " << endl;
    cin >> *(pTestScores + i);
    sum += *(pTestScores + i);
  }
  cout << "testScores: " << testScores << endl;
  cout << "Total for all students: " << sum << endl;
  cout << "Average Score: " << sum / 5 << endl;

  return 0;
}

# Pointing to a Pointer

Besides having a pointer that points to a number or a character, pointers can point to other pointers.
A commonly used example for this type of arrangement is using an arroy of pointers. (Since the array name points to the elements in array, then each element can contain a pointer to the data)

#include "stdafx.h"
#include <iostream>

using namespace std;

int main() {
  // Pointing to Pointer
  int num = 10;
  int* pNum = &num;
  int** p2Num = &pNum;

  cout << "Address of num: " << &num << endl;
  cout << "Address stored in pNum: " << pNum << endl;
  cout << "Address of pNum: " << &pNum << endl;
  cout << "Address stored in p2Num: " << p2Num << endl;

  // Array of Pointers
  int testScores[5] {100, 95, 99, 85, 83};
  int* pointerArray[5];
  for (int i = 0; i < 5; i++) {
    pointerArray[i] = &(testScores[i]);
    cout << pointerArray[i] << endl;
    cout << *(pointerArray[i]) << endl;   // 100, 95, 99, 85, 83
    cout << *(pointerArray + i) << endl;
    cout << **(pointerArray + i) << endl; // 100, 95, 99, 85, 83

  }
  return 0;
}

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