lecture 19 part 2.pdf

8/14/2019 Lecture 19 Part 2.pdf

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1992-2012 by Pearson Education, Inc. & John Wiley & SonsSome portions are adopted from C++ f or Everyone by Horstmann

ENGR 1200U Introduc tion to Programming

Lecture 19 Arrays and Vecto rs

Dr. Eyhab Al-Masri

ENGR 1200UWinter 2013 - UOIT

What is the difference between anargument and a return value?

An argument is an expression that is sent to a function as an input to that function (it appears in the parentheses of a function call)

A return value is a piece of data that is output by a function, and sent back to the calling function.


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What are global constants?

A global constant is a named constant that is available to every function in a program

Global constants are typically used to represent unchanging values that are needed throughout a program


Can you have two local variableswith the same name?

No.

int sum( int num1)

{ int num1 = 0;return num1;

}


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Can you have a local and globalvariables with the same name?

Yes. int num1...

int sum( int num1){

num1 = 0;return num1;

}


What is a static variable?

Sometimes it is desirable for a program to remember what value is stored in a local variable between function calls.

This is accomplished by making the variable static

Static variables are not destroyed when a function returns


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What does it mean to overload afunction?

A Two or more functions may have the same name,

as long as their parameter lists are

different

int square( int number){

return number * number;}

double square( double number){

return number * number;}


When working with a large number of values, it is important to be able tomanage large collections of data

ExampleSuppose we would like to store a set of 100 temperaturemeasurements to be used for perform several computationsSolution- Create different names for the temperature measurements?- Use a method that can work with a group of values?

your best choice is to use rr y


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By using a array, you Can conveniently manage collections of data

Do not have to worry about the details of how they

are stored

Do not worry about how many are in the vector

automatic resizing

so what is the difference between vector and an array ?


The variables you worked with so far are designed tohold only one value at a timeEach of the variable definitions (below) cause onlyenough memory to be reserved to hold one value of the specified data type

ON EPTAn array allows you to store and work withmultiple values of the same data type

int count; Enough memory for 1 int

double price; Enough memory for 1 double

char letter; Enough memory for 1 char

1234

56.5

A


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How it works? An array works like a variable that can store a

group of values, all of the same data type. The values are stored together in consecutive

memory locations.

Examplestring WeekyDays[7]; //enough memory to hold seven string values

Element 0 Element 1 Element 2 Element 3 Element 4 Element 5 Element 6


An array size declarator must be a constantinteger expression with a value greater than 0

It can be either a literal (as in the previous

example) or a named constant, as shown here:

Exampleconst int SIZE = 7; string WeekyDays[SIZE];


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A one-dimensional array can be visualized as

a list of values arranged in either a row or a

column

Individual elements of the array are specified

using the array name and an offset .

In C++ the offset of the first element is always

0 (zero).


WeekDays[0] WeekDays[1] WeekDays[2] WeekDays[3] WeekDays[4] WeekDays[5] WeekDays[6]

Exampleconst int SIZE = 7; string WeekyDays[SIZE];

WeekDays[0]

WeekDays[1]

WeekDays[2]

WeekDays[3]

WeekDays[4]

WeekDays[5]

WeekDays[6]

We assign a type and an identifier to an array and

then distinguish between elements , or values, inthe array using offsets

Offsets are also referred to as indices or subscripts


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Definition Syntax

data_type identifier[array_size] [= initialization_list] ;

Examplesfloat temperature[100]; // Array of 100 floatschar letter[26]; // Array of 26 charactersdouble size[1200]; // Array of 1200 doublesstring name[10]; // Array of 10 string objects


Initializing Arrays

Initializing array elements (initialization=>declaration)char vowels[5] = {'a', 'e', 'i', 'o', 'u'};bool ansKey[] ={ true , true , false , true , false , false };

vowels'a' 'e' 'i' 'o' 'u'

true falsefalsetruefalsetrue

ansKey


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ENGR 1200UWinter 2013 - UOIT Table 6..1: C++ for Everyone by Cay Horstman


CONCEPTIndividual elements of an array are assigned uniquesubscripts. These subscripts are used to access theelements

Individual Variables

Although an entire array has only one name, elementsmay be accessed and used as individual variables

This is possible because each element is assigned a number (or subscript)

A subscript is used as an index to pinpoint a specific element in an array


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ExampleWeekDays[0] = Sunday; // pronounced WeekDays sub zero

Sunday ? ? ? ? ?


?

WeekDays[3] = Wednesday;

Sunday? ?

Wednesday? ?


?


Defining an Array


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ExampleGiven the array:double values[] = { 32, 54, 67.5, 29, 35, 80, 115, 44.5, 100, 65 };

To access the element at index 4using this notation: values[4]

4 is the index (or subscript)

32.0

54.0

67.5

29.0

35.0

80.0

115.0

44.5

100.0

65.0


ExampleGiven the array:

double values[] = { 32, 54, 67.5, 29, 35, 80, 115, 44.5, 100, 65 };

To access the element at index 4using this notation: values[4]

4 is the index (or subscript)

double values[10];

...cout


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Example (contd)The same notation can be used to change the element

values[4] = 17.7; 32.0

54.0

67.5

29.0

35.0

80.0

115.0

44.5

100.0

65.0


Example (contd)The same notation can be used to change the element

values[4] = 17.7; 32.0

54.0

67.5

29.0

17.7

80.0115.0

44.5

100.0

65.0


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Example (contd)That is, the legal elements for the values array are:

values[0] , the first elementvalues[1] , the second elementvalues[2] , the third elementvalues[3] , the fourth elementvalues[4] , the fifth element

...values[9] , the tenth nd l st leg l element

recall: double values[10];

The index must be >= 0 and


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BUGSC++ does not enforce array bounds

Invalid references are NOT reported by the compiler

May or may not result in run-time error

Examples: segmentation fault, bus error

Such errors are often difficult to identify

Results in unpredictable program behavior

lecture 19 part 2.pdf

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