Topic 15
Arrays
1
Displaying a Report
Problem:
We want to process
10
test scores and
display a report.
A sample report is as
follows:
Score
Grade
63
C
92
A
84
A
. . .
. . .
77
B
2
Displaying a Report
Suppose we do it using this method:
cout << "Score\tGrade\n:";
for(int i = 1; i <= 10; i++)
{
cout << "Enter test score " << i << ":
";
cin >> score;
if(score >= 80)
. . .
cout << score << "\t" << grade << endl;
}
3
Displaying a Report
The input/output for this program will be as
follows:
Enter test score 1: 63
63
C
Enter test score 2: 92
92
A
. . .
This method cannot be used to display the
report in the format we want.
4
Displaying a Report
The program must read and store all the
test scores, then process them and display
the report.
We should use
10
variables as follows:
5
Displaying a Report
We read all the
test scores and
store them in the
1
0 variables.
We cannot use a
loop now.
We must use
cin
object
1
0 times.
cout << "Enter test score 1: ";
cin >>
score0
;
cout << "Enter test score 2: ";
cin >>
score1
;
.
.
.
.
cout << "Enter test score 10:
";
cin >>
score9
;
6
Displaying a Report
After we get all
the test scores,
we process
them and
display the
score and the
grade.
We have to
repeat the same
actions
1
0
times.
if(
score0
>= 80)
. . .
cout <<
score0
<< "\t"
<< grade << endl;
if(
score1
>= 80)
. . .
cout <<
score1
<< "\t"
<< grade << endl;
.
.
.
.
7
Displaying a Report
Now the input/output will be as follows:
Enter test score 1: 63
Enter test score 2: 92
. . .
Enter test score 10: 77
Score Grade
63
C
92
A
. . .
77
B
8
Array ConceptBut what if we have many test scores, say 50?
We cannot use this method!A better way is to use an array.An arrayis a collection of elementsthe same data type.An array has a name and a size.
of
9
Array Concept
Example:
Array with
1
0
elements to store
some data values.
Array name – scores
Array size –
1
0
Array name
Array with
10 elements
10
Declaring an ArrayAn array must be declared before it can be used.General format for array declaration:element_type array_name[ array_size ]; Example:int scores[10];array namearray size
11
Declaring an Array
int scores[10];
char name[10];
Array to store 10
integers
Array to store
10
characters (
not a
string
)
12
[9]
Declaring an Array
double gpa[40];
Note:
All the elements are the same data type.
Array to store 40 floating point
numbers
13
Accessing Elements in Arrays
The elements in the
array are arranged
in a sequence.
We can refer to the
elements as the
first
element, the
second
element, and so
forth until we get to
the
last
element.
1
st element
10
th
element
2nd element
.
.
.
.
14
Accessing Elements
Each element in the
array has an
index
.
The indexes are
written in
brackets
([ ]).
The first element has
index 0.
The last element has
index (
array_size - 1
).
inde
x
15
1
st element
10
th
element
2nd element
.
.
.
.
inde
x
Last
element
index is 9
First
element
index is 0
16
Accessing Elements in Arrays
We use the index to refer to an element in the
array.
Example:
if we have an array declaration as
follows:
int scores[
1
0];
Then we can use the indexes as follows:
scores[0] – refers to the
1
st element.
