The document discusses arrays in C++ programming, including how to declare and initialize arrays, access array elements using indexes, and provides examples of programs that read user input into arrays, calculate sums of array elements, and print arrays in reverse order. It also explains common array sorting algorithms like selection and bubble sort and provides examples of their implementation.

1. Lecture 8
Arrays
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2. Objectives
• To Learn about arrays
• Explore how to declare and manipulate data
into arrays
• Understand the meaning of “array index out of
bounds”
• Become familiar with the restrictions on array
processing
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3. Introduction to Arrays
• Given this scenario …
– Write a program that reads five numbers, and
performs some manipulations on these
numbers, such as find their sum, and print the
numbers in reverse order
– We could use five individual variables of type
int, but five variables are hard to keep track of
– We could make program more readable by
giving the variables related names such as
item1, item2, item3, and so forth, but this
solution becomes absurd if the number of items
is very large
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4. Program: Read five numbers, find their sum, and print
the numbers in reverse order
#include <iostream>
using namespace std;
int main()
{
int item0, item1, item2, item3, item4;
int sum;
cout<<"Enter five integers: ";
cin>>item0>>item1>>item2>>item3>>item4 <<endl;
sum = item0 + item1 + item2 + item3 + item4;
cout<<"The sum of the numbers = "<<sum<<endl;
cout<<"The numbers in reverse order are: ";
cout<<item4<<" "<<item3<<" "<<item2<<" " << item1<<" "<<item0<<endl;
return 0;
}
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5. Arrays
Arrays: are a series of elements (variables) of the same type placed consecutively in
memory that can be individually referenced by adding an index to a unique name.
Explanations: This means that, for example, we can store 5 values of type int without
having to declare 5 different variables each with a different identifier. Instead, using an
array we can store 5 different values of the same type, int for example, with a unique
identifier.
For example, an array to contain 5 integer values of type int called item could be
represented this way:
int item[5];
0 1 2 3 4
item
int
where each blank panel represents an element of the array, that in this case are
integer values of type int. These are numbered from 0 to 4 since in arrays the
first index is always 0, independently of its length .
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6. Arrays
Like any other variable, an array must be declared before it is used.
A typical declaration for an array in C++ is:
type name [elements];
where type is a valid object type (int, float...), name is a valid
variable identifier and the elements field, that is enclosed within
brackets [], specifies how many of these elements the array
contains. Therefore, to declare item as shown above it is as simple
as the following sentence:
int item[5];
NOTE: The elements field within brackets [] when declaring an
array must be a constant value, since arrays are blocks of static
memory of a given size and the compiler must be able to determine
exactly how much memory it must assign to the array before any
instruction is considered.
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7. Initializing arrays
When declaring an array of local scope (within a function), if we
do not specify otherwise, it will not be initialized, so its content is
undetermined until we store some values in it. If we declare a
global array (outside any function) its content will be initialized
with all its elements filled with zeros. Thus, if in the global scope
we declare:
int item[5];
every element of item will be set initially to 0:
0 1 2 3 4
item 0 0 0 0 0
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8. Initializing arrays
When we declare an Array, we have the possibility to assign initial
values to each one of its elements using curly brackets { }. For
example:
int item [5] = { 16, 2, 77, 40, 12071 };
This declaration would have created an array like the following one:
0 1 2 3 4
item 16 2 77 44 12071
The number of elements in the array that we initialized within curly brackets { }
must match the length in elements that we declared for the array enclosed within
square brackets [ ].
int item [] = { 16, 2, 77, 40, 12071 };
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9. Program 1: Read five numbers, find their sum, and print
the numbers in reverse order
int main()
{
int item[5]; //declare an array item of five components
int sum=0;
cout<<"Enter five numbers."<<endl;
cin>>item[0] >> item[1] >> item[2] >> item[3] >> item[4] >> item[5] ;
sum = sum + item[0] + item[1] + item[2] + item[3] + item[4] + item[5];
cout<<"The sum of the numbers is: "<<sum<<endl;
cout<<"The numbers in reverse order are: ";
cout<<item[4]<<“ "<<item[3]<<" "<<item[2]<<" "
<< item[1]<<" "<<item[0]<<endl;
return 0;
}
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10. Program 2: Read five numbers, find their sum, and
print the numbers in reverse order
int main()
{
int item[5]; //declare an array item of five components
int sum=0, int counter;
cout<<"Enter five numbers."<<endl;
for(counter = 0; counter < 5; counter++)
{
cin>>item[counter];
sum = sum + item[counter];
}
cout<<"The sum of the numbers is: "<<sum<<endl;
cout<<"The numbers in reverse order are: ";
for(counter = 4; counter >= 0; counter--)
cout<<item[counter]<<" ";
return 0;
}
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11. Program 3: Read five numbers, find and print the
smallest number among them
int main ()
{
double a[10];
double sml;
for (int i=0; i<=4; i++)
cin >> a[i];
sml=a[0];
for (int i=1; i<=4; i++)
{
if (sml > a[i])
sml=a[i];
}
cout << "the smallest number is: " << sml;
getch();
return 0;
}
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12. Access the values of an Array
• The values of an array can be access using following format:
name[index]
• From previous example, item has 5 elements and each of those
elements is of type int
To store the value of 33 in the second element of item:
item[1] = 33;
To pass the value of the second element of item to the variable
temporary:
temporary = item[1];
• Notice that the second element of item is specified item[1], since
first is item[0], therefore, the second is item[1]. By this same
reason, its last element is item[4]. If we write item[5], we will be
acceding to the sixth element of item and therefore exceeding the
size of the array
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13. Access the values of an Array
• In C++ it is perfectly valid to exceed the valid range of indices for
an Array, which can create problems since they do not cause
compilation errors but they can cause unexpected results or
serious errors during execution. The reason why this is allowed
will be seen farther ahead when we begin to use pointers
• At this point it is important to be able to clearly distinguish
between the two uses that brackets [ ] have related to arrays
– To set the size of arrays when declaring them
int item[5]; // declaration of a new Array (begins with a type
name)
– To specify indices for a concrete array element when referring
to it
item[1] = 33; // access to an element of the Array
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14. Sort Algorithm (Selection)
1. Search for the smallest value in the array – the smallest value is the value in a[3]
2. Place the smallest value in a[0], and place the value that was in a[0] in a[3], the
location where the smallest was found
3. Starting at a[1], find the smallest remaining value, swap it with the value
currently in a[1]
4. Starting at a[2], continue the process until the array is sorted
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15. int main () for (int k=0; k<=3; k++)
{ {
double a[5]; sml=a[k];
double sml, temp; Psml=k;
int Psml; //index of small for (int i=k; i<=4; i++)
if (sml > a[i])
for (int i=0; i<=4; i++) {
{ sml=a[i];
cout << “enter a[“<< i <<“] ” ; Psml=i;
cin >> a[i]; }
} temp=a[Psml];
cout << "nthe current array "; a[Psml]=a[k];
for (int i=0; i<=4; i++) a[k]=temp;
cout << a[i] << 't'; }
cout << "nthe sorted array: ";
for (int i=0; i<=4; i++)
cout << a[i] << 't';
return 0;
}
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16. Sort Algorithm (Bubble)
#include <iostream> for (i=0; i<=4; i++)
using namespace std; for (j=0; j<=3; j++)
if (a[j]>a[j+1])
int main () {
{ temp=a[j];
int a[5]; a[j]=a[j+1];
int i,j, temp; a[j+1]=temp;
}
for (int i=0; i<=4; i++) cout << "nthe sorted array: ";
{ for (i=0; i<=4; i++)
cout << "enter a["<< i <<"] "; cout << a[i] << 't';
cin >> a[i];
} return 0;
}
cout << "nthe current array ";
for (int i=0; i<=4; i++)
cout << a[i] << 't';
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17. Sequential Search Algorithm
• Sequential search is to determine the index i position
of an object ‘X’ in an array A
int search (const int a[], int
target 8 number_used, int target)
{
[0] [1] [2] [3] [4] [5] [6] [7]
int index = 0;
bool found = false;
a 2 7 3 8 4 12 9 5 while ((!found) && (index <
number_used))
if (target == a[index])
Found “8” in position 4 found = true;
else
index++;
if (found)
return index;
else
return -1;
}
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18. THE END
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