Array_part1

BITG 1113: Array (Part 1)

LECTURE 8 1

Objectives :  To understand basic concepts of array.

 To understand how to use arrays in the program.  To know how to input values into array and output values from array.  To know how to use array as function parameter. 2

Concepts • An array is a sequenced collection of elements of the same name and the same type. • It serve as an example of structured data types - they are effectively just lists of variables all of the same data type ("int", "char" or whatever).

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Example : An array of Numbers

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Concepts • When referring to which element in array, we use the subscript concept – E.g : numbers1 – number[1] – This is also known as indexing the elements • Loops can be used to read and write, also it can be used to add, subtract, multiply and divide the elements in arrays • The subscript starts with 0 E.g : number[0] for the first element

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Using arrays in C++

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Read or Print using index

Example of an array flowchart 7

Declaring and defining arrays • The general syntax for an array declaration is: – < identifier name>[<size>]; – Declaration and definition tells the compiler the name of the array, type of each element and size or number of element in the array

• E.g : suppose we are writing a program to manipulate data concerning the number of hours a group of 6 employees have worked in a particular week. •

We might start the program with the array declaration: int hours[6];

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Declaring and defining arrays

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Initialization

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Inputting Values • Is another way to fill the array • Can be done using a loop – the most appropriate is for loop • E.g :

int scores[10]; for ( i = 0; i < 10; i++) cin >> scores [i];

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Outputting values • Usually done by using a for loop E.g : for (i=0; i<10; i++) cout << scores[i];

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Assigning values • Individual elements can be assigned values using the assignment operator – E.g : scores [4] = 23; • We can copy an array to another array with the same size and type but it is wrong to assign one array to another : – E.g : int num1[5]={1,2,3,4,5},num2; num2=num1; //error

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Assigning values • Example : to copy elements of num1 into num2. int num1[5] = {1,2,3,4,5}, num2[5]; for(int i =0 ; i<5;i++) { num2[i]= num1[i]; //correct }

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Example : Input and Output of an array #include #include using namespace std; void main() { int i, ary1[5]={2,4,6,8,10},ary2[5],ary3[5]; cout<<“Enter 5 numbers:\n”; for(i=0; i<5; i++) cin>>ary2[i]; cout<<setw(15)<<“ary1”<<setw(10)<<“ary2”<<setw(10) <<“ary3”<<endl; for(i=0;i<5;i++) { ary3[i]= ary1[i]+ ary2[i]; cout<<setw(15)<<ary1[i]<<setw(10)<<ary2[i] <<setw(10)<<ary3[i]<<endl; } }

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Output : Enter 5 numbers: 1 2 3 4 5 ary1

ary2

ary3

2

1

3

4

2

6

6

3

9

8

4

12

10

5

15 16

Example : Determine the minimum value #include using namespace std; void main() { int i, score[5], min; cout<<“Enter 5 scores:\n”; for(i=0; i<5; i++) cin>>score[i]; min = score[0];

Output : Enter 5 scores: 85 60 55 78 95

for(i=1;i<5;i++) The minimum score is 55 { if(score[i]< min ) min = score[i]; } cout<<“The lowest score is “ << min; }

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Exchanging values – the wrong way

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Exchanging values – using temporary variable

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Example : Exchanging values #include using namespace std; void main() { int temp; int numbers[5] = {3,7,12,24,45}; cout << "Before exchange the value :"<< endl; for(int i=0; i<5; i++) cout << numbers[i] << ' '; temp = numbers[3]; numbers[3] = numbers[1]; numbers[1] = temp; cout<<"\nAfter exchange the value :"<<endl; for(int i=0; i<5; i++) cout << numbers[i] << ' '; cout << endl; }

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Array Applications • Common statistical application using array – Frequency distributions and histograms • Frequency array – Shows number of identical element in a series of number • Histograms – A pictorial representation of a frequency array

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Frequency array

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Frequency histogram

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Two dimensional array • An array that consists of rows and columns – In C++ it means an array of two-dimensional array

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Two dimensional array • Two dimensional array declaration int table [5][4]; • First dimension specifies the number of rows in the array • Second dimension specifies the number of columns in each row

• Initialization int table [5][4] = {0,1,2,3,10,11,12,13,20,21,22,23,30,31,32, 31,40,41,42,43};

int table [5][4] = {{0,1,2,3},{10,11,12,13}, {20,21,22,23}, {30,31,32,31},{40,41,42,43}}; int table [5][4] = {{0,1},{10},{20,21,22},{30}, {40,41,42,43}};

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Inputting Values • for(r=0;r<5;r++) for(c=0;c<4;c++) cin>>table[r][c];

Outputting Values  for(r=0;r<5;r++){ for(c=0;c<4;c++) cout<
Accessing Values •

To access the element of a two dimensional array, the index of row and column are used. E.g : To print the element in the second row and the third column of table. int table [5][4] = {{0,1,2,3},{10,11,12,13},{20,21,22,23}, {30,31,32,31},{40,41,42,43}}; cout<
•

Individual elements can be initialized using the assignment operator. table[2][0] = 23;

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Accessing Values • Let us assume that we want to initialize our 5 x 4 array as shown below. 0 10 20 30 40

1 11 21 31 41

2 12 22 32 42

3 13 23 33 43

• The following code will perform the initialization : int table[5][4]; for(r=0;r<5;r++) for(c=0;c<4;c++) table[r][c]= r*10 + c ;

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Example: Two Dimensional array #include using namespace std; void main() { int i,j,ary1[4][3]; for(i=0; i<4; i++){ cout << “Enter 3 numbers for row :"<>ary1[i][j]; cout<<endl; } cout<<“Elements of ary1 is : ”<<endl; for(i=0; i<4; i++){ for(j=0; j<3; j++) cout<<ary1[i][j]<<setw(5); cout<<endl; }

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Output : Enter 3 numbers for row 1 : 1 2 3 Enter 3 numbers for row 2 : 2 4 6 Enter 3 numbers for row 3 : 3 6 9 Enter 3 numbers for row 4 : 4 8 12

Elements of ary1 is : 1 2 3 2 4 6 3 6 9 4 8 12

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