EKT120_LECTURE07_ARRAYS1

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UniMAP Sem II - 09/10 EKT120 : Computer Programming 1

Lecture 7Arrays (1)


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What is an Array? The variables that we have used so far have all

common characteristics: Each variable could only store a single value at a

time. Example:

int count, length, num;double average, total;char selection, choice;

An array is a collection of a fixed number ofcomponents wherein all of the components are of thesame type


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What is an Array? (Example) Example: Let us work with a list of five

integers:

5, 10, 15, 20, and 25. Previously we would declare five

variables:int num1, num2, num3, num4, num5;

By using array, since they are all of thesame data type, we could just write:int num[5];


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What is an Array? (Example)

5

10

15

20

25

num

num[0]

num[1]

num[2]

num[3]

num[4]

5 components or elements in

this array.

Elements are referred to index.

Element num[2] has index 2and value 15.


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Arrays of Data Engineering applications usually involve large

chunk of data (of common type)

Arrays provide easy and efficient concept fordata storage or management

Arrays are usually processed through loops(processing is very common)

Arrays are accessed by indicating an addressor index


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Arrays in CArrays can assume any type (including

the primitive data types)

int, char, string, double, float, etc.

Like any other instances, arrays mustbe declared before use.


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Multiple Instances vs. Array// multiple instanceint value1, value2, value3;

printf (Enter first value: );

scanf (%d, &value1);

printf(Enter second value: );scanf(%d, &value2);

printf (Enter third value: );scanf(%d, &value3);

// process or display

// arrayint valueArray[3];

for(int count=0;count


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Arrays - Memory Allocation Arrays are allocated

bulk memory

Single reference usedfor multiple locations

Items are accessed

based on index(address) withreference to first item


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Arrays Arithmetic Operations on arrays are similar to that

on basic variables.

sum = num[0] + num[1] + num[2] +

num[3];

mult = 3 * num[1];

remainder = num[3] % 3;

total = num[1] * num[2];


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Array Initialization Arrays can be initialized directly, but assignments are

done using loops

Like any other simple variable, arrays can also beinitialized while they are being declared.

double sales[5] = {12.25, 32.50, 16.90, 23, 45.68};

sales[0]=12.25, sales[1]= 32.50, sales[2]=16.90,sales[3]= 23.00, sales[4]=45.68;


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Array Initialization (cont) Initializers:

If not enough initializers, rightmost element becomes 0

int n[ 7 ] = { 1, 2, 3, 4, 5 }; => n[5] = n[6] = 0

All elements = 0

int n[ 5 ] = { 0 };

If size is omitted, initializers determine the size

int n[ ] = { 1, 2, 3, 4, 5 };5 initializers, therefore 5 element array


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Sample Program#include int main()

{int a[3]= {11,22}, b[]={44, 55, 66},i;double x[2],y[10];

printf("a[0]=%2d, a[1]=%2d, a[2]=%2d \n""b[0]=%2d, b[1]=%2d, b[2]=%2d \n\n",

a[0],a[1],a[2],b[0],b[1],b[2]);

printf("Please enter two real numbers\n");scanf("%lf %lf",&x[0], &x[1]);printf("x[0] = %.1lf x[1] = %.1lf\n\n", x[0], x[1]);

for (i=0;i


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Sample Program Output:

a[0]=11, a[1]=22, a[2]= 0b[0]=44, b[1]=55, b[2]=66

Please enter two real numbers77.0 88.0x[0] = 77.0 x[1] = 88.0

y[0]=0.00y[1]=100.00y[2]=200.00y[3]=300.00

y[4]=400.00y[5]=500.00y[6]=600.00y[7]=700.00y[8]=800.00y[9]=900.00


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Array Initialization DuringDeclaration

When declaring and initializing arrays, it isnot necessary to specify the size of the

array. The size of the array is determined by the

number of initial values in the braces.

double sales[] = {12.25, 32.50, 16.90, 23, 45.68};


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A simple example

The program declares and initializes thearray y. It uses a for loop with index i to

access the successive elements of y. Foreach loop iteration, the value accessed id isadded to the variable total which is finallydisplayed. Note that the loop index i starts

from 0 to 4 (not from 1 to 5). Also, note thatthe array size n is declared in the definestatement.


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A simple example (cont..)

#include#define n 5 // define number of n in the array

void main(){

int i, total = 0; // variable declarationint y[n]={9,6,20,5,12}; // array declaration and

// initializationfor (i=0;i


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Notes

The defined constants, #define is used to easeany future amendments of the codes, for

instance, if the array is to be widen to an nof 10instead of 5, it would be adequate by modifyingthe line:

#define n 5 #define n 10

there is no need to make any other changes tothe program, thus making the life of programmereasier.


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Operations on Array

Reading data in an array

for (index = 0; index < 10; index++)

scanf (%d, &sale[index]);

Printing an arrayfor (index = 0; index < 10; index++)

printf (%d , sale[index]);


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Parallel Arrays

Two (or more) arrays are calledparallel if their corresponding

components hold related information.int student_Id[50];

char student_Grade[50];


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Multi-Dimensional Arrays

Arrays can have multiple dimensions

Most used is the 2-dimensional array

(for matrix implementation)

Actual implementation is a single array(segmented)

Nested loopstructure usually used toaccess items


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Multi-Dimensional Arrays(cont..)

A collection of the same type of datastored in contiguous and increasing

memory locations. Declaration of multi-dimensional array:

int b[2][3] = {51, 52, 53, 54, 55, 56};

array_type array_name Array dimension = 2

two rows

three columns first rowinitial values

second rowinitial values


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Multi-Dimensional Arrays(cont..)

can use braces ({ }) to separate rows in 2-dimensional arrays. For example:

int c [4][3] = {{1, 2, 3},{4, 5, 6},{7, 8, 9},{10,11,12}};

int c [4][3] = {{1, 2},{4, 5, 6},{7},{10,11,12}};

initializes c[0][2], c[2][1] and c[2][2] to be zero

int c [ ][3] = {{1, 2, 3},{4, 5, 6},{7, 8, 9},{10,11,12}};

implicitly declares the number of rows to be 4

4 rows

3 columns

rows

columns


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Notes on Arrays

Arrays enable better and easier datamanagement system

Closely related to loops Indexing is zero-based

(0 to n-1 for an array with n locations)

Multi-dimensional arrays requirenested loopstructure

(e.g. 2-dimensional array)


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Index out of bounds

Out of bounds is when (index < 0) or

(index > arraySize - 1)

It is a run-time error, happens when anindex is outside the valid boundaries ofthe array. Example:

int a[10]; int x = 10a[9] = 3 ; //ok

a[x] = 4 ; //10 is not within the range 0..9


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Index out of bound

In C, no guard against this problem

Does not check whether index value is

within range or not Can result in accessing data of wrong

memory location


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EndArrays (1)

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EKT120_LECTURE07_ARRAYS1