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Arrays
CS 308 – Data Structures

One-Dimensional Arrays
• A list of values with the same data type that
are stored using a single group name (array
name).
• General array declaration statement:
data-type array-name[number-of-items];
• The number-of-items must be specified
before declaring the array.
const int SIZE = 100;
float arr[SIZE];

• Individual elements of the array can be
accessed by specifying the name of the
array and the element's index:
arr[3]
• Warning: indices assume values from 0 to
number-of-items -1!!
One-Dimensional Arrays (cont.)

One-Dimensional Arrays (cont.)
arr[0] arr[1] arr[2] arr[3] arr[4]
Skip over 3 elements to get
the starting location of
element 3
The array name arr identifies
the starting location of the array
Start here
element 3

1D Array Initialization
• Arrays can be initialized during their declaration
int arr[5] = {98, 87, 92, 79, 85};
int arr[5] = {98, 87} - what happens in this case??
• What is the difference between the following two
declarations ?
char codes[] = {'s', 'a', 'm', 'p', 'l', 'e'};
char codes[] = "sample";
codes[0] codes[1] codes[2] codes[3] codes[4] codes[5] codes[6]
s a m p l e 0

Two-dimensional Arrays
• A two-dimensional array consists of both rows
and columns of elements.
• General array declaration statement:
data-type array-name[number-of-rows][number-of-columns];

• The number-of-rows and number-of-columns must
be specified before declaring the array.
const int ROWS = 100;
const int COLS = 50;
float arr2D[ROWS][COLS];
• Individual elements of the array can be accessed
by specifying the name of the array and the
element's row, column indices.
arr2D[3][5]
Two-dimensional Arrays (cont.)

2D Array Initialization
• Arrays can be initialized during their
declaration
int arr2D[3][3] = { {98, 87, 92}, {79, 85, 19},
{32, 18, 2} };
• The compiler fills the array row by row
(elements are stored in the memory in the
same order).

1D Arrays as Arguments
• Individual array elements are passed to a
function in the same manner as other
variables.
max = find_max(arr[1], arr[3]);
• To pass the whole array to a function, you
need to specify the name of the array only!!

#include <iostream.h>
float find_average(int [], int);
void main()
{
const numElems = 5;
int arr[numElems] = {2, 18, 1, 27, 16};
cout << "The average is " << find_average(arr, numElems) << endl;
}
float find_average(int vals[], int n)
{
int i;
float avg;
avg=0.0;
for(i=0; i<n; i++)
avg += vals[i];
avg = avg/n;
return avg;
}

• Important: this is essentially "call by
reference":
a) The name of the array arr stores the address of the
first element of the array arr[0] (i.e., &arr[0]).
b) Every other element of the array can be accessed by
using its index as an offset from the first element.
1D Arrays as Arguments (cont.)
arr[0] arr[1] arr[2] arr[3] arr[4]
The starting address of arr array is &arr[0].
This is passed to the function find_average()

2D Arrays as Arguments
• Individual array elements are passed to a function
in the same manner as other variables.
max = find_max(arr2D[1][1], arr2D[1][2]);
• To pass the whole array to a function, you need to
specify the name of the array only!!
• The number of columns must be specified in the
function prototype and function header.

#include <iostream.h>
float find_average(int [][2], int, int);
void main()
{
const numRows = 2;
const numCols = 2;
int arr2D[numRows][numCols] = {2, 18, 1, 27};
float average;
average = find_average(arr2D, numRows, numCols);
cout << "The average is " << average << endl;
}

float find_average(int vals[][2], int n, int m)
{
int i,j;
float avg;
avg=0.0;
for(i=0; i<n; i++)
for(j=0; j<m; j++)
avg += vals[i][j];
avg = avg/(n*m);
return avg;
}

• Important: this is essentially "call by
reference":
a) The name of the array arr2D stores the address
of arr2D[0] (i.e., &arr2D[0])
b) arr2D[0] stores the address of the first element
of the array arr2D[0][0] (&arr2D[0][0])
c) Every other element of the array can be
accessed by using its indices as an offset from
the first element.
2D Arrays as Arguments (cont.)

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