1. 310201 Fundamental Programming
More on Arrays

2. Review simple variables hold a single value
in the previous class we saw that arrays hold a collection of related values
also in the last class, we saw the basics of declaring, initialising and using arrays
in a C++ array, the first value in an array is held at position 0, not 1

3. More on Arrays
in this class we cover some more of the details of implementing arrays in C++
some jargon
more on initialisation
more on referencing arrays
a common error using arrays
passing arrays to functions
passing array elements to functions

4. Some Jargon Used With Arrays
element : a value held in an array
index : an integer value that refers to an element in an array; we say C++ arrays are zero- indexed – the first position is zero
subscript : can be used instead of index – as in “subscript out of range”; can also be used to describe the expression that appears between the brackets to refer to an element in an array
dimension : the number of elements in an array - the size of the array – as in “the dimensions of my office are 3 meters by 4; the room size”
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

5. More on Initialising Arrays
if the array size is omitted when it is declared, the compiler can automatically determine the size from initial values
int Primes[] = {1, 3, 5, 7, 11};
is equivalent to
int Primes[5] = {1, 3, 5, 7, 11};
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

6. More on Referencing Arrays
we normally use an integer literal, or an integer variable, to refer to a value of interest in an array
Results[0]
Results[ResultNbr]
also, an integer expression can be used
Results[CurrentPos - 1]
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

7. A Common Error Using Arrays
a common error when using arrays is to refer to an element that does not exist
that is: to use an index value that is outside the acceptable range...
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

8. Activity
can you see how this code refers to an array element that does not exist?
const NBR_RESULTS = 3;
int Results[NBR_RESULTS] = {0};
for (int ResultNbr = 0;
ResultNbr <= NBR_RESULTS;
ResultNbr++)
cout << Results[ResultNbr];
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

9. Activity Break

10. Activity Feedback
in the last trip through the loop below, the code refers to Results[3], which does not exist
const int NBR_RESULTS = 3;
int Results[NBR_RESULTS] = {0};
for (int ResultNbr = 0;
ResultNbr <= NBR_RESULTS;
ResultNbr++)
cout << Results[ResultNbr] << endl;
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

11. A Common Error Using Arrays
C++ does not give an error when using an index value that is out-of-range
it is the programmer’s responsibility to ensure that array references are always within the acceptable range
if, in an expression, you refer to an array element that does not exist:
results are unpredictable – the program may give erroneous output, or go into an infinite loop
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

12. A Common Error Using Arrays
if you assign a value to an array element that does not exists:
with luck, you’ll get a memory violation error – so you know there’s a problem
without luck, results are unpredictable:
erroneous output produced
infinite loops lock-up the program
memory used by the operating system is overwritten causing a system crash
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

13. Passing Arrays to Functions
arrays are always passed to functions by reference – but, no ampersand (&) appears before the parameter name
consider a program using an array called Results as shown on the next slide...
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

14. Passing Arrays to Functions
main
Results
NbrResults
Results
Results
NbrResults
GetResults
DisplayResults
Results
NbrResults
SortResults
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

15. notes: here, the maximum number of results is defined
void GetResults(int Results[], int &NbrResults);
void SortResults(int Results[], int NbrResults);
void DisplayResults(int Results[], int NbrResults);
const int MAX_NBR_RESULTS = 10;
void main (void) {
int Results[MAX_NBR_RESULTS] = {0},
NbrResults = 0;
GetResults(Results, NbrResults);
SortResults(Results, NbrResults);
DisplayResults(Results, NbrResults); }
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.
notes: here, the maximum number of results is defined
as a global constant – it is used to define the size of
the Results array and will also be used to avoid an
out-of-range error in the GetResults function

16. notes: the NbrResults parameter is an output of the
void GetResults(int Results[], int &NbrResults);
void SortResults(int Results[], int NbrResults);
void DisplayResults(int Results[], int NbrResults);
const int MAX_NBR_RESULTS = 10;
void main (void) {
int Results[MAX_NBR_RESULTS] = {0},
NbrResults = 0;
GetResults(Results, NbrResults);
SortResults(Results, NbrResults);
DisplayResults(Results, NbrResults); }
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.
notes: the NbrResults parameter is an output of the
GetResults function, so an ampersand appears before
its name in the GetResults header and declaration

17. notes: the Results array is also an output of the
void GetResults(int Results[], int &NbrResults);
void SortResults(int Results[], int NbrResults);
void DisplayResults(int Results[], int NbrResults);
const int MAX_NBR_RESULTS = 10;
void main (void) {
int Results[MAX_NBR_RESULTS] = {0},
NbrResults = 0;
GetResults(Results, NbrResults);
SortResults(Results, NbrResults);
DisplayResults(Results, NbrResults); }
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.
notes: the Results array is also an output of the
GetResults function, but an ampersand does not appear
before its name in GetResults header and declaration

18. notes: square brackets appear in header and declaration
void GetResults(int Results[], int &NbrResults);
void SortResults(int Results[], int NbrResults);
void DisplayResults(int Results[], int NbrResults);
const int MAX_NBR_RESULTS = 10;
void main (void) {
int Results[MAX_NBR_RESULTS] = {0},
NbrResults = 0;
GetResults(Results, NbrResults);
SortResults(Results, NbrResults);
DisplayResults(Results, NbrResults); }
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.
notes: square brackets appear in header and declaration
to show that a parameter is an array

19. notes: square brackets do not appear in the function call
void GetResults(int Results[], int &NbrResults);
void SortResults(int Results[], int NbrResults);
void DisplayResults(int Results[], int NbrResults);
const int MAX_NBR_RESULTS = 10;
void main (void) {
int Results[MAX_NBR_RESULTS] = {0},
NbrResults = 0;
GetResults(Results, NbrResults);
SortResults(Results, NbrResults);
DisplayResults(Results, NbrResults); }
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.
notes: square brackets do not appear in the function call

20. notes: one does not need to specify the size of an array
void GetResults(int Results[], int &NbrResults);
void SortResults(int Results[], int NbrResults);
void DisplayResults(int Results[], int NbrResults);
const int MAX_NBR_RESULTS = 10;
void main (void) {
int Results[MAX_NBR_RESULTS] = {0},
NbrResults = 0;
GetResults(Results, NbrResults);
SortResults(Results, NbrResults);
DisplayResults(Results, NbrResults); }
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.
notes: one does not need to specify the size of an array
that appears as a parameter in a function header or
declaration – it is normal practice to not specify the size
of a parameter that is an array

21. notes: however, called functions need to know how many
void GetResults(int Results[], int &NbrResults);
void SortResults(int Results[], int NbrResults);
void DisplayResults(int Results[], int NbrResults);
const int MAX_NBR_RESULTS = 10;
void main (void) {
int Results[MAX_NBR_RESULTS] = {0},
NbrResults = 0;
GetResults(Results, NbrResults);
SortResults(Results, NbrResults);
DisplayResults(Results, NbrResults); }
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.
notes: however, called functions need to know how many
values have been stored in the array

22. Passing Arrays to Functions
the DisplayResults function may look like this…
void DisplayResults(int Results[], int NbrResults) {
cout << "Results: " << endl;
for (int ResultNbr = 0;
ResultNbr < NbrResults;
ResultNbr++)
cout << " Result[" << ResultNbr
<< "]: " << Results[ResultNbr] << endl; }
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

23. Passing Arrays to Functions
it is possible to protect the elements of an array passed as an input to a function:
put const in front of the parameter declaration
any attempt by the function to assign a value to the array will result in an error when compiled
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.
void DisplayResults(const int Results[],
int NbrResults)

24. Activity
an interesting, and timely, example of passing an array to a function is shown on the next slide
what output do you think this program will produce?
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

25. #include <iostream.h>
void Transform(char Array[], int NbrElements);
void main (void) {
const int NBR_CHARS = 3;
char Name[NBR_CHARS] = {'I','B','M'};
int Index;
cout << "Name before Transform is: " ;
for (Index = 0; Index < NBR_CHARS; Index++)
cout << Name[Index];
Transform(Name, NBR_CHARS);
cout << endl << "Name after Transform is: " ;
cout<<Name[Index]; }
void Transform(char Array[], int NbrElements)
for (int Index = 0; Index < NbrElements; Index++)
--Array[Index];
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

26. Activity Break

27. Activity Feedback output produced by this program is:
recall that characters are stored as an integer - the following will output H
char MyChar = 'I';
cout << --MyChar;
you may know that the computer in 2001: A Space Odyssey was called HAL
Name before Transform is: IBM
Name after Transform is: HAL

28. Passing Arrays Elements to Functions
the previous example showed how to pass an entire array to a function
we can also pass a single array element to a function
whole arrays are always reference parameters
individual elements of an array can be passed as a value or reference parameter
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

29. Activity what output do you think the following code will produce?
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

30. Activity #include <iostream.h>
void PassByValue(int ArrayElement);
void PassByReference(int &ArrayElement);
void main(void) {
int Marks[3] = {10,20,30};
PassByValue(Marks[0]);
PassByReference(Marks[1]);
for (int Mark = 0; Mark <= 2; Mark++)
cout << “Marks[“ << Mark << “]: “ << Marks[Mark] << endl; }
void PassByValue(int ArrayElement)
ArrayElement++;
void PassByReference(int &ArrayElement)
How can a datagram be transmitted across a physical network that does not understand the datagram format?
IP Datagram is encapsulated in a hardware frame
Placed entirely in the Data area of the frame
Hardware does not examine or change the contents of the data area.

31. Activity Break

32. Activity Feedback output produced by this program is: Marks[0]: 10

33. Activity
write a function named Smallest, that accepts an array of double precision real numbers, and returns the smallest value stored in the array

34. Activity Break

35. Summary in this class we covered: some of the jargon used with arrays
automatic sizing of arrays from initial values
non-integer array references
referencing non-existing array elements
assignment to non-existing array elements
passing arrays to functions
passing arrays elements to functions