Arrays Par Ti

8/8/2019 Arrays Par Ti

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C++ Arrays


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Array Basics An array is a block of contiguous

memory locations to hold values ofa single specified type.

Arrays can hold values of ANY type

In C++, arrays are 0-based. Thismeans that the first element hasindex 0.


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Declaring an Array

To declare an array, use thefollowing structure

type VariableName [ SIZE ];

Example:

int myArray[5];declares an array named myArraythat can hold 5 integers with

indices 0, 1, 2, 3, and 4.


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Declaring an Array

Note: We are using static arrays.

IE the size must be set when thearray is declared, and can notchange during the course of theprogram.

Use constant variables for thearrays size so that modifications tothe size can be made in one place.


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Using an Array In C++, the name of the array

refers to the address of the firstelement in the array.

In order to access an element inthe array, follow the name of the

array with square bracketscontaining the elements index.


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Using an ArrayIn our example, int myArray[5];declares an array of 5 integers.

M32 M36 M40 M44 M48

myArray[0] myArray[1] myArray[2] myArray[3] myArray[4]


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Using an Array Declaring an array does not

automatically initialize the values.

We can initialize our array in thedeclaration statement by assigningit a list of values. The list must be

held in braces, {}. The values inthe list must be separated bycommas.


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Using an ArrayExample:

int myArray[5] = {14,3,7,0,1};

Note: You can only initialize the

array with a list in the arraydeclaration.


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Using an Array If we are initializing an array of

numeric values, any values left outof the list will be set to 0.

Example: int Array[5] = {14};

14 0 0 0 0


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Using an Array You can leave out the size of the

array when using a list to initializethe array in the declaration. Thearrays size will be the number ofvalues in the initialization list.

Example:

int Array[] = {14, 3, 6, 9, 2};

14 3 6 9 2


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Using an Array

To read values into a non-characterarray, use a counter controlled loop

to move through the array indices.Example:

for( int i = 0; i < 5; ++i )

{cout > myArray[ i ];

}


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Using an Array

To output the values in a non-character array, use a counter

controlled loop to move throughthe array indices.

Example:

for ( int i = 0; i < 5; ++i){

cout


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Using an Array Common Error: Overstepping the

bounds of an array.

Your compiler will not produce anerror if an index is used outside ofthe 0 to size 1 range.

Invalid indices are used as anyother, moving the specified offsetfrom the first element in the array.


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Using an Array Overstepping an arrays bounds

can attempt to modify values in

memory locations being used byother variables or programs.


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Using an Array

Example:

int myArray[] = {1,2,3,4,5};

for ( int i = 0; i


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Passing Arrays to Functions

To specify an array argument,place a set of empty bracketsbeside the arrays data type in thefunctions parameter list (forsingle-subscripted arrays).

Example:

void doubleValues( int [], int );


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When calling the function, use thename of the array (no brackets) asan argument of the function.

Example:

int myArray[8]={1,2,3,4,5,6,7,8};

doubleValues( Array, 8 );


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When passing an array argumentto a function were sending theaddress of the first element in thearray, allowing the function directaccess to the array elements.

Remember the Principle of LeastPrivilege! You can make array andreference parameters constant.

void printArray( const int [], int );


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Searching Arrays

Unsorted arrays linear search.

Linear Search Method

Start at one end of the array.

If the current element contains thesearch value, return its array index

If not, move to the next element.

Continue until the element is foundor there are no more elements to

examine.


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Searching Arrays

Sorted arrays binary search.

Binary Search

If the middle element containsthe value youre searching forreturn its array index.

Else, if the middle element islarger than the value youresearching for, search the leftsub-array.

Else search the right sub-array.


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Sorting Arrays

Bubble Sort - Informal Algorithm

Start at the end of the array

swapping all pairs of unorderedelements until you reach thebeginning of the array.

Now the smallest element is at thefront.

Repeat the process until all of theelements are in order.


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Sorting Arrays

Selection Sort - Informal Algorithm

front = position 0

Find the smallest element and swap itto the front. Increment the front

Repeat until front = size - 1

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