C Arrays.ppt

PGT 106 : C PROGRAMMING 1
Lecture 7 – Arrays (1)

Outline
1. Introduction
2. Arrays of Data
3. Array Declaration
4. Array Initialization
5. Operations on Array
6. Multidimensional Arrays
7. Index out of bound

What is an Array?
 An array is a collection/group of a fixed number of
components wherein all of the components are of the
same type referred to a same name

What is an Array? (Example)
 Example: 5, 10, 15, 20, and 25.
 Previously we would declare five
variables:
int iNum1, iNum2, iNum3, iNum4, iNum5;
 By using array,
int aiNum[5];

What is an Array? (Example)
5
10
15
20
25
aiNum
aiNum[0]
aiNum[1]
aiNum[2]
aiNum[3]
aiNum[4]
 5 components or
elements
 Elements are referred to
index.
 Element aiNum[2] has
index 2 and value 15.

Arrays of Data
 Engineering applications usually involve large
chunk of data (of common type)
 Arrays provide easy and efficient concept for
data storage or management
 Arrays are usually processed through loops
(processing is very common)
 Arrays are accessed by indicating an address
or index/subscript

Arrays in C
 Arrays can take any type (including the
primitive data types)
int, char, string, double, float, etc.
 Like any other instances, arrays must
be declared before use.

Array Declaration
 Format:
 data_type array_name [int value];
 int aiList[5];
 const int Max_Size = 10;
int aiHours[Max_Size];
 const int SIZE = 100;
double adAmount[SIZE];
 const int Max_List_Size = 6;
char acAlp[Max_List_Size];
 #define N 10
double adB[N];

Multiple Instances vs. Array
// multiple instance
int iValue1, iValue2, iValue3,
iValue4, iValue 5;
printf (“Enter first value: “);
scanf (“%d”, &iValue1);
printf(“Enter second value: “);
scanf(“%d”, &iValue2);
printf (“Enter third value: “);
scanf(“%d”, &iValue3);
printf (“Enter fourth value: “);
scanf(“%d”, &iValue4)
printf (“Enter fifth value: “);
scanf(“%d”, &iValue5)

UniMAP Sem II -
09/10 PGT 106 : C PROGRAMMING 10
// array
int aiValue[3];
for(int iCount=0; iCount<3; iCount++)
{
printf (“Enter value : ”);
printf (“%d : ”, iCount+1);
scanf (“%d”, &aiValue[iCount]);
}

Arrays - Memory Allocation
 Arrays are allocated
bulk memory
 Single reference used
for multiple locations
 Items are accessed
based on index
(address) with
reference to first item
int aiValue[8];
aiValue[0]=23;
aiValue[1]=56;
aiValue[2]=100;
aiValue[3]=0;
aiValue[4]=12;
aiValue[5]=234;
aiValue[6]=666;
aiValue[7]=4;
23
56
100
0
12
234
666
4
index aiValue
0
1
2
3
4
5
6
7

Arrays Arithmetic
 Operations on arrays are similar to that on
basic variables.
 iSum = aiNum[0] + aiNum[1] + aiNum[2]
+ aiNum[3];
 iMult = 3 * aiNum[1];
 iRemainder = aiNum[3] % 3;
 iTotal = aiNum[1] * aiNum[2];

Array Initialization
 Arrays can be initialized directly, but assignments are
done using loops
 Like any other simple variable, arrays can also be
initialized while they are being declared.
double adSales[5] = {12.25, 32.50, 16.90, 23, 45.68};
adSales[0]=12.25, adSales[1]=32.50,
adSales[2]=16.90, adSales[3]=23.00,
adSales[4]=45.68;

Array Initialization (cont…)
 Initializers:
 If not enough initializers, rightmost element becomes 0
int aiN[ 7 ] = { 1, 2, 3, 4, 5 }; => aiN[5] = aiN[6] = 0
 All elements = 0
int aiN[ 5 ] = { 0 } ;
▪ If size is omitted, initializers determine the size
int aiN[ ] = { 1, 2, 3, 4, 5 };
5 initializers, therefore 5 element array

Sample Program
#include <stdio.h>
int main()
{
int aiA[3]= {11,22}, aiB[]={44, 55, 66},iLoop;
double adX[2],adY[10];
printf(“aiA[0]=%2d, aiA[1]=%2d, aiA[2]=%2d n"
“aiB[0]=%2d, aiB[1]=%2d, aiB[2]=%2d nn",
aiA[0],aiA[1],aiA[2],aiB[0],aiB[1],aiB[2]);
printf("Please enter two real numbersn");
scanf("%lf %lf",&adX[0], &adX[1]);
printf(“adX[0] = %.1lf adX[1] = %.1lfnn", adX[0], adX[1]);
for (iLoop=0;iLoop<10;iLoop++)
{
adY[iLoop]= iLoop*100.0;
printf(“adY[%1d]=%.2lfn", iLoop, adY[i]);
}
return 0;
}
Using a loop to fill all the
elements of the adY[] array.
Initializes the first 2 elements of the
aiA[]array. All the other elements are
then automatically set to zero
Because no array size is given (the
brackets are empty) and three values are
given in braces, the array is
automatically declared to have a size of
3 with the value shown being the initial
element values.

Sample Program
 Output:
aiA[0]=11, aiA[1]=22, aiA[2]= 0
aiB[0]=44, aiB[1]=55, aiB[2]=66
Please enter two real numbers
77.0 88.0
adX[0] = 77.0 adX[1] = 88.0
adY[0]=0.00
adY[1]=100.00
adY[2]=200.00
adY[3]=300.00
adY[4]=400.00
adY[5]=500.00
adY[6]=600.00
adY[7]=700.00
adY[8]=800.00
adY[9]=900.00

Array Initialization During
Declaration
 When declaring and initializing arrays, it is not
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 adSales[] = {12.25, 32.50, 16.90, 23, 45.68};

A simple example
 The program declares and initializes the
array aiY. It uses a ‘for’ loop with index iLoop
to access the successive elements of aiY. For
each loop iteration, the value accessed id is
added to the variable iTotal which is finally
displayed. Note that the loop index iLoop
starts from 0 to 4 (not from 1 to 5). Also,
note that the array size n is declared in the
define statement.

A simple example (cont..)
#include<stdio.h>
#define n 5 // define number of n in the array
void main()
{
int iLoop, iTotal = 0; // variable declaration
int aiY[n]={9,6,20,5,12}; // array declaration and
// initialization
for (iLoop=0;iLoop<n;iLoop++)
iTotal = iTotal + aiY[i];
printf ("nTotal = %dn”, iTotal);
}

Notes
 The defined constants, #define is used to ease
any future amendments of the codes, for
instance, if the array is to be widen to an n of 10
instead of 5, it would be adequate by modifying
the line:
#define n 5  #define n 10
there is no need to make any other changes to
the program, thus making the life of programmer
easier.

Operations on Array
 Reading data in an array
for (iIndex = 0; iIndex < 10; iIndex++)
scanf (“%d”, &aiSale[iIndex]);
 Printing an array
for (iIndex = 0; iIndex < 10; iIndex++)
printf (“%d ”, aiSale[iIndex]);

Parallel Arrays
 Two (or more) arrays are called
parallel if their corresponding
components hold related information.
int aiStudentId[50];
char acStudentGrade[50];

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 loop structure usually used to
access items

2-Dimensional Array
(Example)
5
index aiValue
0
1
2
3
4
5
6
7
5
Column
0 1
0
1
2
3
Row
Address Resolution = Row*(MaxCol) + Col
Row 0
Row 1
int aiValue[4][2];
aiValue[2][1]=5;

(cont..)
 A collection of the same type of data
stored in contiguous and increasing
memory locations.
 Declaration of multi-dimensional array:
 int aiB[2][3] = {51, 52, 53, 54, 55, 56};
array_type array_name Array dimension = 2
two rows
three columns first row
initial values
second row
initial values

(cont..)
 Multi-dimensional array can be initialized directly in
the declaration statement.
 For example:
 int aiB[2][3] = {51, 52, 53, 54, 55, 56};
which initializes the elements to be
aiB[0][0] = 51 aiB[0][1] = 52 aiB[0][2] = 53
aiB[1][0] = 54 aiB[1][1] = 55 aiB[1][2] = 56
* note that C begins its subscripts at 0. The rightmost
subscript is incremented first.

(cont..)
 can use braces ({ }) to separate rows in 2-dimensional arrays.
 For example:
 int aiC [4][3] = {{1, 2, 3},
{4, 5, 6},
{7, 8, 9},
{10,11,12}};
 int aiC [4][3] = {{1, 2},
{4, 5, 6},
{7},
{10,11,12}};
initializes aiC[0][2], aiC[2][1] and aiC[2][2] to be zero
 int aiC [ ][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

Notes on Arrays
 Arrays enable better and easier data
management system
 Closely related to loops
 Indexing is zero-based
(0 to n-1 for an array with n locations)
 Multi-dimensional arrays require
nested loop structure
(e.g. 2-dimensional array)

Index out of bounds
 ‘Out of bounds’ is when (index < 0) or
(index > arraySize - 1)
 It is a run-time error, happens when an
index is outside the valid boundaries of the
array. Example:
int aiA[10]; int iX = 10
aiA[9] = 3 ; //ok
aiA[iX] = 4 ; //10 is not within the range 0..9

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

How to overcome?
 Use defined loops
for (iLoop = 0; iLoop < 10; iLoop ++)
aiList [ iLoop ] = 0;

End – Arrays (1)
Q & A!

C Arrays.ppt

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