1. EKT150 : Computer Programming
Lecture 7 – Arrays (1)
UniMAP Sem I - 10/11
EKT150 : Computer Programming

2. EKT150 : Computer Programming
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
UniMAP Sem I - 10/11
EKT150 : Computer Programming

3. EKT150 : Computer Programming
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 of components wherein all of the components are of the same type
UniMAP Sem I - 10/11
EKT150 : Computer Programming

4. 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 the same data type, we could just write:
int num[5];
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5. What is an Array? (Example)
num
5 components or elements in this array.
Elements are referred to index.
Element num[2] has index 2 and value 15. 5 10 15 20 25
num[0]
num[1]
num[2]
num[3]
num[4]
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6. EKT150 : Computer Programming
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
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7. EKT150 : Computer Programming
Arrays in C
Arrays can assume any type (including the primitive data types)
int, char, string, double, float, etc.
Like any other instances, arrays must be declared before use.
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8. EKT150 : Computer Programming
Array Declaration
Format:
data_type array_name[int value];
Example:
int list[5];
const int Max_List_Size = 10;
int hours[Max_List_Size];
const int SIZE = 100;
double amount[SIZE];
const int Max_List_Size = 6;
char alphas[Max_List_Size];
#define N 10
double b[N];
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9. Multiple Instances vs. Array
int 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
// array
int valueArray[3];
for(int count=0;count<3;count++) {
printf (“Enter value : ”);
printf (“%d : ”, count+1);
scanf (“%d”, &valueArray[count]); }
// process or display
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10. 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
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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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12. EKT150 : Computer Programming
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 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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13. 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
Initializes the first 2 elements of the a[]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 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<10;i++)
y[i]= i*100.0;
printf("y[%1d]=%.2lf\n", i, y[i]); }
return 0;
Using a loop to fill all the elements of the y[] array.
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15. EKT150 : Computer Programming
Sample Program
Output:
a[0]=11, a[1]=22, a[2]= 0
b[0]=44, b[1]=55, b[2]=66
Please enter two real numbers
x[0] = x[1] = 88.0
y[0]=0.00
y[1]=100.00
y[2]=200.00
y[3]=300.00
y[4]=400.00
y[5]=500.00
y[6]=600.00
y[7]=700.00
y[8]=800.00
y[9]=900.00
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16. 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 sales[] = {12.25, 32.50, 16.90, 23, 45.68};
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17. EKT150 : Computer Programming
A simple example
The program declares and initializes the array y. It uses a ‘for’ loop with index i to access the successive elements of y. For each loop iteration, the value accessed id is added to the variable total which is finally displayed. Note that the loop index i starts from 0 to 4 (not from 1 to 5). Also, note that the array size n is declared in the define statement.
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18. A simple example (cont..)
#include<stdio.h>
#define n 5 // define number of n in the array
void main() {
int i, total = 0; // variable declaration
int y[n]={9,6,20,5,12}; // array declaration and // initialization
for (i=0;i<n;i++)
total = total + y[i];
printf ("\nTotal = %d\n”, total); }
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19. EKT150 : Computer Programming
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.
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20. EKT150 : Computer Programming
Operations on Array
Reading data in an array
for (index = 0; index < 10; index++)
scanf (“%d”, &sale[index]);
Printing an array
printf (“%d ”, sale[index]);
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21. EKT150 : Computer Programming
Parallel Arrays
Two (or more) arrays are called parallel if their corresponding components hold related information.
int student_Id[50];
char student_Grade[50];
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22. 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
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23. 2-Dimensional Array (Example)
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24. 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 b[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
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EKT150 : Computer Programming

25. Multi-Dimensional Arrays (cont..)
Multi-dimensional array can be initialized directly in the declaration statement.
For example:
int b[2][3] = {51, 52, 53, 54, 55, 56};
which initializes the elements to be
b[0][0] = 51 b[0][1] = 52 b[0][2] = 53
b[1][0] = 54 b[1][1] = 55 b[1][2] = 56
* note that C begins its subscripts at 0. The rightmost subscript is incremented first.
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26. 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},
initializes c[0][2], c[2][1] and c[2][2] to be zero
int c [ ][3] = {{1, 2, 3},
implicitly declares the number of rows to be 4
3 columns
4 rows
rows
columns
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27. EKT150 : Computer Programming
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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28. EKT150 : Computer Programming
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 a[10]; int x = 10
a[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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How to overcome?
Use defined loops
for (i = 0; i < 10; i ++)
list [ i ] = 0;
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31. EKT150 : Computer Programming
End – Arrays (1)
Q & A!
UniMAP Sem I - 10/11
EKT150 : Computer Programming