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

2. 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
PGT 106 : C PROGRAMMING

3. What is an Array? Same data type Same name
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
Same data type
Same name
PGT 106 : C PROGRAMMING

4. 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];
PGT 106 : C PROGRAMMING

5. What is an Array? (Example)
5 components or elements
Elements are referred to index.
Element aiNum[2] has index 2 and value 15.
aiNum 5 10 15 20 25
aiNum[0]
aiNum[1]
aiNum[2]
aiNum[3]
aiNum[4]
PGT 106 : C PROGRAMMING

6. 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
PGT 106 : C PROGRAMMING

7. 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.
PGT 106 : C PROGRAMMING

8. Array Declaration data_type array_name [int value]; Format:
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];
PGT 106 : C PROGRAMMING

9. Multiple Instances vs. Array
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)
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]); }
UniMAP Sem II - 09/10
PGT 106 : C PROGRAMMING

11. 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;
index aiValue 1 2 3 4 5 6 7 23 56
100 12
234
666 4
PGT 106 : C PROGRAMMING

12. 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];
PGT 106 : C PROGRAMMING

13. 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;
PGT 106 : C PROGRAMMING

14. 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
PGT 106 : C PROGRAMMING

15. Sample Program #include <stdio.h> int main() {
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.
#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 \n\n",
aiA[0],aiA[1],aiA[2],aiB[0],aiB[1],aiB[2]);
printf("Please enter two real numbers\n");
scanf("%lf %lf",&adX[0], &adX[1]);
printf(“adX[0] = %.1lf adX[1] = %.1lf\n\n", adX[0], adX[1]);
for (iLoop=0;iLoop<10;iLoop++)
adY[iLoop]= iLoop*100.0;
printf(“adY[%1d]=%.2lf\n", iLoop, adY[i]); }
return 0;
Using a loop to fill all the elements of the adY[] array.
PGT 106 : C PROGRAMMING

16. 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
adX[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
PGT 106 : C PROGRAMMING

17. 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};
PGT 106 : C PROGRAMMING

18. 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.
PGT 106 : C PROGRAMMING

19. 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 = %d\n”, iTotal); }
PGT 106 : C PROGRAMMING

20. 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.
PGT 106 : C PROGRAMMING

21. Operations on Array Reading data in an array
for (iIndex = 0; iIndex < 10; iIndex++)
scanf (“%d”, &aiSale[iIndex]);
Printing an array
printf (“%d ”, aiSale[iIndex]);
PGT 106 : C PROGRAMMING

22. Parallel Arrays
Two (or more) arrays are called parallel if their corresponding components hold related information.
int aiStudentId[50];
char acStudentGrade[50];
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23. 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
PGT 106 : C PROGRAMMING

24. 2-Dimensional Array (Example)
int aiValue[4][2];
aiValue[2][1]=5;
index aiValue 1 2 3 4 5 6 7 5
Row 0
Row 1
Column 1 2 3 5
Row
Address Resolution = Row*(MaxCol) + Col
PGT 106 : C PROGRAMMING

25. Multi-Dimensional Arrays (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
PGT 106 : C PROGRAMMING

26. Multi-Dimensional Arrays (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.
PGT 106 : C PROGRAMMING

27. Multi-Dimensional Arrays (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},
initializes aiC[0][2], aiC[2][1] and aiC[2][2] to be zero
int aiC [ ][3] = {{1, 2, 3},
implicitly declares the number of rows to be 4
3 columns
4 rows
rows
columns
PGT 106 : C PROGRAMMING

28. 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)
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29. 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
PGT 106 : C PROGRAMMING

30. 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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31. How to overcome? Use defined loops
for (iLoop = 0; iLoop < 10; iLoop ++)
aiList [ iLoop ] = 0;
PGT 106 : C PROGRAMMING

32. End – Arrays (1)
Q & A!
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