Topics to Cover

• Static arrays
• cin.get()/fin.get() does not skip any whitespace character
• Practice with structs

Static Arrays

Dynamic arrays vs static arrays

int A[6];

int* A = new int[6];

Not possible. 

int* B = new int[10];
for(int i=0; i<6; i++)
  B[i] = A[i];
delete [] A;
A = B;

Here's a simple toy program that uses a static array.

#include <iostream>
using namespace std;
void foo(int n);

int main()
{
  int n;
  cin >> n;
  foo(n);

  return 0;
}

void foo(int n)
{
  cout << "Enter " << n << " numbers: ";

  int A[n];
  for(int i=0; i<n; i++)
    cin >> A[i];

  cout << "The numbers in reverse: " << endl;
  for(int i=n-1; i>=0; i--)
    cout << A[i] << " ";
  cout << endl;

  // control_point_1
}

~$ ./a.out
4
Enter 4 numbers: 1 3 0 7
The numbers in reverse:
7 0 3 1

Q: For a static array A, do you have to delete [] A;, when you don't need it anymore?

No. As shown in the above diagram, the array is inside the stack frame
of function foo(). When foo() returns, the entire array will be discarded
automatically. 

Using Static Arrays in struct Definitions

• (Names of the week) If you wanted to hardcode the names of the days of the week into a program, you know the size will be 7, so there's no point in making a dynamic array.
• (Vertices of a quadrilateral) Consider a program that uses an array to store the vertices of a quadrilateral. Since we know that a quadrilateral always has exactly four vertices, we could use static arrays.

  
  struct Quad
  {
    char label;
    point vert[4];
  };
  

Difference between dynamic and static arrays

To understand the difference between this version of Quad and the previous version, consider this picture:

Note:

• In the dynamic version, the pointer (instead of the array) is embedded in the Quad object; the array is outside of the Quad object, somewhere else in memory.
• In the static version, the entire array vert is embedded in the Quad object.

The above picture really tells you all you need to know to understand the difference between using static and dynamic arrays ... when you really can use static arrays.

Q: Can you change the contents of a static array?

A: Of course, yes

Quick check

Q (0,0) (1,0) (1,1) (0,1)
Q (0,0) (1,0) (1,1) (0,1)
P (1,0) (2,0) (2,1) (1,1)

Q (0,0) (1,0) (1,1) (0,1)
Q (1,0) (2,0) (2,1) (1,1)
P (1,0) (2,0) (2,1) (1,1)

// step 1
Quad S;
...       // S has 'Q' and (0,0), (1,0), (1,1), and (0,1) 
print(S); // It will print Q (0,0) (1,0) (1,1) (0,1)

// step 2
Quad R;
R = S;    // Copying will have different meanings!
R.label = 'P';    

// step 3
for(int i = 0; i < 4; i++)
  R.vert[i].x++;

print(S);
print(R);

Dynamic Version	Static Version

cin.get() and fin.get()

int get();

• The function reads a character from the input and returns the ASCII code of the letter.
• More importantly, it will also read whitespace charcters.

#include <iostream>
using namespace std;
int main()
{
  int N = 10;
  char* A = new char[N];
  for(int i=0; i < N; i++)
    cin >> A[i];
      
  for(int i=0; i < N; i++)
    cout << A[i];
  cout << endl;

  delete [] A;
  return 0;
}

#include <iostream>
using namespace std;
int main()
{
  int N = 10;
  char* A = new char[N];
  for(int i=0; i < N; i++)
    A[i] = cin.get();
      
  for(int i=0; i < N; i++)
    cout << A[i];
  cout << endl;

  delete [] A;
  return 0;
}

$ ./ex
* *   *   *    *    *  * * *  *
**********

$ ./ex2
* *   *   *    *    *  * * *  *
* *   *   

Where would it be useful?

Other sample program?

Mandatory Practice Problem

• You have the file BankAccts.txt, which lists all your bank account information at the beginning of the year.
• You also have the file Transactions.txt, which lists all the deposit transactions for the year. Each transaction consists of
  • the date
  • the account number, and
  • the $'s deposited.

$ ./a.out
11265   Jones   $225.18
15233   Smith   $2593.24
17677   Adams   $395.56
18820   Moon    $803.9
20011   Zoom    $5432.68
20202   Howe    $6464.93
21300   Grace   $1334.72
22544   Putnam  $4124.9
23003   Jones   $4129.55
24404   Marion  $6600.31