Lecture#8 introduction to array with examples c++

EC-102 Computer System &
Programming
Lecture #8
Instructor: Jahan Zeb
Department of Computer Engineering (DCE)
College of E&ME

Introduction
 Arrays
– Structures of related data items
– Static entity (same size throughout program)

Arrays
 Array
– Consecutive group of memory locations
– Same name and type (int, char, etc.)
 To refer to an element
– Specify array name and position number (index)
– Format: arrayname[ position number ]
– First element at position 0
 N-element array c
c[ 0 ], c[ 1 ] … c[ n - 1 ]
– Nth element as position N-1

Arrays
 Array elements like other variables
– Assignment, printing for an integer array c
c[ 0 ] = 3;
cout << c[ 0 ];
 Can perform operations inside subscript
c[ 5 – 2 ] same as c[3]

Arrays
c[6]
-45
6
0
72
1543
-89
0
62
-3
1
6453
78
Name of array (Note that
all elements of this array
have the same name, c)
c[0]
c[1]
c[2]
c[3]
c[11]
c[10]
c[9]
c[8]
c[7]
c[5]
c[4]
Position number of the
element within array c

Declaring Arrays
 When declaring arrays, specify
– Name
– Type of array
• Any data type
– Number of elements
– type arrayName[ arraySize ];
int c[ 10 ]; // array of 10 integers
float d[ 3284 ]; // array of 3284 floats
 Declaring multiple arrays of same type
– Use comma separated list, like regular variables
int b[ 100 ], x[ 27 ];

Examples Using Arrays
 Initializing arrays
– For loop
• Set each element
– Initializer list
• Specify each element when array declared
int n[ 5 ] = { 1, 2, 3, 4, 5 };
• If not enough initializers, rightmost elements 0
– To set every element to same value
int n[ 5 ] = { 0 };
– If array size omitted, initializers determine size
int n[] = { 1, 2, 3, 4, 5 };
• 5 initializers, therefore 5 element array

1
2 // Initializing an array.
3 #include <iostream>
4
5 using std::cout;
6 using std::endl;
7
8 #include <iomanip>
9
10 using std::setw;
11
12 int main()
13 {
14 int n[ 10 ]; // n is an array of 10 integers
15
16 // initialize elements of array n to 0
17 for ( int i = 0; i < 10; i++ )
18 n[ i ] = 0; // set element at location i to 0
19
20 cout << "Element" << setw( 13 ) << "Value" << endl;
21
22 // output contents of array n in tabular format
23 for ( int j = 0; j < 10; j++ )
24 cout << setw( 7 ) << j << setw( 13 ) << n[ j ] << endl;
25
Declare a 10-element array of
integers.
Initialize array to 0 using a
for loop. Note that the array
has elements n[0] to n[9].

26 return 0; // indicates successful termination
27
28 } // end main
Element Value
0 0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0

1
2 // Initializing an array with a declaration.
4
5 using std::cout;
6 using std::endl;
7
9
10 using std::setw;
11
12 int main()
13 {
14 // use initializer list to initialize array n
15 int n[ 10 ] = { 32, 27, 64, 18, 95, 14, 90, 70, 60, 37 };
16
18
19 // output contents of array n in tabular format
20 for ( int i = 0; i < 10; i++ )
21 cout << setw( 7 ) << i << setw( 13 ) << n[ i ] << endl;
22
24
25 } // end main
Note the use of the initializer
list.

Element Value
0 32
1 27
2 64
3 18
4 95
5 14
6 90
7 70
8 60
9 37

Examples Using Arrays
 Array size
– Can be specified with constant variable (const)
• const int size = 20;
– Constants cannot be changed
– Constants must be initialized when declared
– Also called named constants or read-only variables

1
2 // Initialize array s to the even integers from 2 to 20.
4
5 using std::cout;
6 using std::endl;
7
9
10 using std::setw;
11
12 int main()
13 {
14 // constant variable can be used to specify array size
15 const int arraySize = 10;
16
17 int s[ arraySize ]; // array s has 10 elements
18
19 for ( int i = 0; i < arraySize; i++ ) // set the values
20 s[ i ] = 2 + 2 * i;
21
23
Note use of const keyword.
Only const variables can
specify array sizes.
The program becomes more
scalable when we set the array
size using a const variable.
We can change arraySize,
and all the loops will still
work (otherwise, we’d have to
update every loop in the
program).

24 // output contents of array s in tabular format
25 for ( int j = 0; j < arraySize; j++ )
26 cout << setw( 7 ) << j << setw( 13 ) << s[ j ] << endl;
27
29
30 } // end main
Element Value
0 2
1 4
2 6
3 8
4 10
5 12
6 14
7 16
8 18
9 20

1
2 // Using a properly initialized constant variable.
4
5 using std::cout;
6 using std::endl;
7
8 int main()
9 {
10 const int x = 7; // initialized constant variable
11
12 cout << "The value of constant variable x is: "
13 << x << endl;
14
16
17 } // end main
The value of constant variable x is: 7
Proper initialization of
const variable.

1
2 // A const object must be initialized.
3
4 int main()
5 {
6 const int x; // Error: x must be initialized
7
8 x = 7; // Error: cannot modify a const variable
9
11
12 } // end main
d:cpphtp4_examplesch04Fig04_07.cpp(6) : error C2734: 'x' :
const object must be initialized
Uninitialized const results
in a syntax error. Attempting
to modify the const is
another error.

1
2 // Compute the sum of the elements of the array.
4
5 using std::cout;
6 using std::endl;
7
8 int main()
9 {
11
12 int a[ arraySize ] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
13
14 int total = 0;
15
16 // sum contents of array a
17 for ( int i = 0; i < arraySize; i++ )
18 total += a[ i ];
19
20 cout << "Total of array element values is " << total << endl;
21
23
24 } // end main
Total of array element values is 55

1
2 // Histogram printing program.
4
5 using std::cout;
6 using std::endl;
7
9
10 using std::setw;
11
12 int main()
13 {
15 int n[ arraySize ] = { 19, 3, 15, 7, 11, 9, 13, 5, 17, 1 };
16
17 cout << "Element" << setw( 13 ) << "Value"
18 << setw( 17 ) << "Histogram" << endl;
19
20 // for each element of array n, output a bar in histogram
21 for ( int i = 0; i < arraySize; i++ ) {
22 cout << setw( 7 ) << i << setw( 13 )
23 << n[ i ] << setw( 9 );
24
25 for ( int j = 0; j < n[ i ]; j++ ) // print one bar
26 cout << '*';
Prints asterisks corresponding
to size of array element,
n[i].

27
28 cout << endl; // start next line of output
29
30 } // end outer for structure
31
33
34 } // end main
Element Value Histogram
0 19 *******************
1 3 ***
2 15 ***************
3 7 *******
4 11 ***********
5 9 *********
6 13 *************
7 5 *****
8 17 *****************
9 1 *

Lecture#8 introduction to array with examples c++

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