1. CS149D Elements of Computer Science
Ayman Abdel-Hamid
Department of Computer Science
Old Dominion University
Lecture 22: 11/14/2002
Lecture 22: 11/14/2002
CS149D Fall 2002

2. Outline Arrays (section 5.1) Declaration and initialization
Accessing array elements
Arrays and data files
Lecture 22: 11/14/2002
CS149D Fall 2002

3. Arrays 1 variable can store 1 data value.
How about if we want to deal with 100 integers or 100 doubles (100 measurements) at the same time? Declare 100 variables (How about 1000?)
One Solution
We use an array to store a number of elements of the same data type
A one-dimensional array is a number of successive memory locations, each of which can store an item of data of the same type and which are all referenced through the same variable name.
Example a values array
How many array elements (array size)?
First element is values[0]
Last element is values[5]
values[0]
values[1]
values[2]
values[3]
values[4]
values[5]
Lecture 22: 11/14/2002
CS149D Fall 2002

4. Arrays Declaration and Initialization
Syntax to declare an array
Data Type Array_Name [Array Size];
int values[6]; array index ranges from 0 to 5 (6-1)
double elements[5]; array index ranges from 0 to ?
Can initialize array when defined
int values[6] = {0,1,2,3,4,5};
values[0]
values[1]
values[2]
values[3]
values[4]
values[5]
Initialization sequence shorter than array size
int values[6] = {0};
values[0]
values[1]
values[2]
values[3]
values[4]
values[5]
values[0]
values[1]
values[2]
values[3]
No size, but an initialization sequence
int values[] = {0,1,2,3};
Lecture 22: 11/14/2002
CS149D Fall 2002

5. Accessing Array elements1/2
Fill an array with numbers 0,2,4,6,8,10,12 (0*2, 1*2,3*2, …)
//define array
const int SIZE = 7; // Why did we choose SIZE as 7?
int values[SIZE];
//assign values to array elements
for (int k = 0; k < SIZE ; k++)
values[k] = k *2;
//print array
for (int k = 0 ; k < SIZE ; k++)
cout << values[k] << “\t”;
Lecture 22: 11/14/2002
CS149D Fall 2002

6. Accessing Array elements2/2
Printing an array in reverse order
for (int k = SIZE - 1 ; k >= 0 ; k--)
cout << values[k] << “\t”;
No check is performed that array index lies within the bounds of the array!
int values[5]; // index bounds from 0 to 4
cout << values[5]; //What happens in this case?
Reading from a file and assigning to array elements
A file with 2 fields per line (id grade) id is an int and grade is a float
const int SIZE = 20;
int id[20];
float grade[20];
fstream gradesf;
gradesf.open(“GradesFile”,ios::in);
for (k=0 ; k < SIZE; k++)
gradesf >> id[k] >> grade[k];
Lecture 22: 11/14/2002
CS149D Fall 2002