Arrays

Arrays are collections of like items which are referenced by position, not by name

One-Dimensional Arrays

Arrays of Records

Two-Dimensional Arrays

One-Dimensional Arrays

A one-dimensional array is a collection of variables – all of the same type – in which the first part of the variable name is the same, and the last part is an index value enclosed in square brackets. Example: string

The declaration of a one-dimensional array is similar to the declaration of a simple variable with one exception, you must also declare the size of the array.

Example: int value[1000]; The variables are value[0] – value[999]

Syntax Templates

ArrayDeclaration

DataType ArrayName [ConstIntExpression];

ArrayComponentAccess

ArrayName [ Index Expression ]

The index expression may be as simple as a constant or a variable name or as complex as a combination of variables, operators, and function calls.

Array Examples

Consider the following declarations:

float angle[4];

int testScore[10];

and the assignments:

angle[0] = 4.93; angle[2] = 0.5;

angle[1] = -15.2; angle[3] = 1.67;

Each array component can be treated exactly the same as any simple variable of type float.

Ex: angle[2] = 9.6;

      cin >> angle[2];

    cout << angle[2];

y = sqrt(angle[2]);

   x = 6.8 * angle[2] + 7.5;

Out-of-Bounds Array Indexes

Problem: Given the declaration

float alpha[100],

valid indexes for the array range from 0 – 99. What happens if you access alpha[105], for example?

Answer: C++ does not check for out-of-bounds indexes either at compile time or at run time. The memory location is destroyed. It is entirely the programmer’s responsibility to make sure that an array does not step off either end of the array.

More About Arrays

Arrays can be initialized in their declarations.

Example: int age[5] = {23, 10, 16, 37, 12};

C++ does not allow aggregate operations on arrays. To copy one array into another, you must do it yourself, element by element. You also may not do an aggregate comparison of arrays. It’s not possible to return an entire array as the value of a value-returning function. You can pass an entire array as an argument to a function.

Examples of Declaring and
Accessing Arrays

const int BUILDING_SIZE = 350;

int occupants[BUILDING_SIZE];

int totalOccupants;

int counter;

totalOccupants = 0;

for (counter = 0; counter < BUILDING_SIZE; counter++)

totalOccupants = totalOccupants + occupants[counter];

enum Drink {ORANGE, COLA, ROOT_BEER, GINGER_ALE, CHERRY, LEMON};

float salesAmt[6];

for (flavor = ORANGE; flavor <= LEMON; flavor = Drink(flavor + 1))

cout << salesAmt[flavor] << endl;

Passing Arrays as Arguments

By default, C++ simple variables are always passed by value.

Arrays are always passed by reference.

Example:

void ZeroOut (/* out */ float arr[],

/* in */ int numElements)

{

int i;

for (i = 0; i < numElements; i++)

arr[i] = 0.0

}

Preventing the Function
from Modifying an Array

Use the reserved word const.

Example:

void Copy(/* out */      int destination[],

    /* in */ const int source[],

       /* in */       int size)

{

int i;

for (i = 0; i < size; i++)

destination[i] = source[i];

}

Arrays of Records

Many applications require a collection of records.

Example:

   const int MAX_STUDENTS = 150;

      enum GradeType {A, B, C, D, F};

      struct StudentRec

      {

         string stuName;

         float gpa;

         int examScore[4];

         GradeType courseGrade;

      };

      StudentRec gradeBook[MAX_STUDENTS];

      int count;

Arrays of Records

Valid assignment statements given the declaration of gradeBook

    gradeBook[55].gpa = 4.0;

      gradeBook[103].stuName = “Harold Schmerdlap”;

      gradeBook[149].examScore[0] = 83;

      gradebook[0].GradeType = B;

      for (count = 0; count < MAX_STUDENTS; count++)

         cout << gradeBook[count].stuName << endl;

Two-Dimensional Arrays

A two-dimensional array is used to represent items in a table with rows and columns of the same data type item.

Each component is accessed using two indices that represent the position in each dimension.

ArrayDeclaration

DataType Array Name [ConstInt Expression] [ConstIntExpression] … ;

ArrayComponentAccess

ArrayName[Index Expression]

[Index Expression] …;

Two-Dimensional Array Examples

const int NUM_ROWS = 100;

const int NUM_COLS = 9;

float alpha[NUM_ROWS][NUM_COLS];

Two-Dimensional Array Examples

const int NUM_ROWS = 100;

const int NUM_COLS = 9;

float alpha[NUM_ROWS][NUM_COLS];

int hiTemp[52][7];

Two-Dimensional Array Examples

const int NUM_ROWS = 100;

const int NUM_COLS = 9;

float alpha[NUM_ROWS][NUM_COLS];

int hiTemp[52][7];

enum Colors {RED, ORANGE, YELLOW, GREEN, BLUE, INDIGO, VIOLET};

enum Makes {FORD, TOYOTA, HYUNDAI, JAGUAR, CITROEN, BMW, FIAT, SAAB};

float crashRating[7][8];

crashRating[BLUE][JAGUAR] = 0.83;

crashRating[RED][FORD] = 0.19;

Processing Two-Dimensional Arrays

Process the rows.

Process the columns.

Initialize the array.

Print the array.


	Arrays are collections of like items which are referenced by position, not by name
		One-Dimensional Arrays
		Arrays of Records
		Two-Dimensional Arrays


	A one-dimensional array is a collection of variables – all of the same type – in which the first part of the variable name is the same, and the last part is an index value enclosed in square brackets. Example: string
	The declaration of a one-dimensional array is similar to the declaration of a simple variable with one exception, you must also declare the size of the array.
	Example: int value[1000]; The variables are value[0] – value[999]


	ArrayDeclaration
	DataType ArrayName [ConstIntExpression];

	ArrayComponentAccess
	ArrayName [ Index Expression ]

	The index expression may be as simple as a constant or a variable name or as complex as a combination of variables, operators, and function calls.


	Consider the following declarations:
	float angle[4];
	int testScore[10];

	and the assignments:
	angle[0] = 4.93; angle[2] = 0.5;
	angle[1] = -15.2; angle[3] = 1.67;

	Each array component can be treated exactly the same as any simple variable of type float.

	Ex: angle[2] = 9.6;
	cin >> angle[2];
	cout << angle[2];
	y = sqrt(angle[2]);
	x = 6.8 * angle[2] + 7.5;


	Problem: Given the declaration
	float alpha[100],
	valid indexes for the array range from 0 – 99. What happens if you access alpha[105], for example?
	Answer: C++ does not check for out-of-bounds indexes either at compile time or at run time. The memory location is destroyed. It is entirely the programmer’s responsibility to make sure that an array does not step off either end of the array.


	Arrays can be initialized in their declarations.
		Example: int age[5] = {23, 10, 16, 37, 12};
	C++ does not allow aggregate operations on arrays. To copy one array into another, you must do it yourself, element by element. You also may not do an aggregate comparison of arrays. It’s not possible to return an entire array as the value of a value-returning function. You can pass an entire array as an argument to a function.


	const int BUILDING_SIZE = 350;
	int occupants[BUILDING_SIZE];
	int totalOccupants;
	int counter;
	totalOccupants = 0;
	for (counter = 0; counter < BUILDING_SIZE; counter++)
	totalOccupants = totalOccupants + occupants[counter];


By default, C++ simple variables are always passed by value.
Arrays are always passed by reference.
	Example:

		void ZeroOut (/* out */ float arr[],
		/* in */ int numElements)
		{
			int i;
			for (i = 0; i < numElements; i++)
				arr[i] = 0.0
		}


	Use the reserved word const.
	Example:
	void Copy(/* out */ int destination[],
	/* in */ const int source[],
	/* in */ int size)
	{
	int i;
	for (i = 0; i < size; i++)
	destination[i] = source[i];
	}


	Many applications require a collection of records.
	Example:
	const int MAX_STUDENTS = 150;
	enum GradeType {A, B, C, D, F};
	struct StudentRec
	{
	string stuName;
	float gpa;
	int examScore[4];
	GradeType courseGrade;
	};

	StudentRec gradeBook[MAX_STUDENTS];
	int count;


	Valid assignment statements given the declaration of gradeBook

	gradeBook[55].gpa = 4.0;
	gradeBook[103].stuName = “Harold Schmerdlap”;
	gradeBook[149].examScore[0] = 83;
	gradebook[0].GradeType = B;

	for (count = 0; count < MAX_STUDENTS; count++)
	cout << gradeBook[count].stuName << endl;


	A two-dimensional array is used to represent items in a table with rows and columns of the same data type item.
	Each component is accessed using two indices that represent the position in each dimension.
	ArrayDeclaration
		DataType Array Name [ConstInt Expression] [ConstIntExpression] … ;
	ArrayComponentAccess
		ArrayName[Index Expression]
		[Index Expression] …;


	const int NUM_ROWS = 100;
	const int NUM_COLS = 9;
	float alpha[NUM_ROWS][NUM_COLS];


	Process the rows.
	Process the columns.
	Initialize the array.
	Print the array.