C++ Arrays

C++ array stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

Instead of declaring individual variables, such as number0, number1, ..., and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and ..., numbers[99] to represent individual variables. A specific element in an array is accessed by an index.

All arrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.

Declaring Arrays

To declare an array in C++, the programmer specifies the type of the elements and the number of elements required by an array as follows −

 type arrayName [ arraySize ]; 

This is called a single-dimension array. The arraySize must be an integer constant greater than zero and type can be any valid C++ data type. For example, to declare a 10-element array called balance of type double, use this statement −

 double balance[10]; 

Initializing Arrays

You can initialize C++ array elements either one by one or using a single statement as follows −

 double balance[5] = {1000.0, 2.0, 3.4, 17.0, 50.0}; 

The number of values between braces { } can not be larger than the number of elements that we declare for the array between square brackets [ ]. Following is an example to assign a single element of the array −

If you omit the size of the array, an array just big enough to hold the initialization is created. Therefore, if you write −

 double balance[] = {1000.0, 2.0, 3.4, 17.0, 50.0}; 

You will create exactly the same array as you did in the previous example.

 balance[4] = 50.0; 

The above statement assigns element number 5^th in the array a value of 50.0. Array with 4^th index will be 5^th, i.e., last element because all arrays have 0 as the index of their first element which is also called base index. Following is the pictorial representaion of the same array we discussed above −

Accessing Array Elements

An element is accessed by indexing the array name. This is done by placing the index of the element within square brackets after the name of the array. For example −

 double salary = balance[9]; 

The above statement will take 10^th element from the array and assign the value to salary variable. Following is an example, which will use all the above-mentioned three concepts viz. declaration, assignment and accessing arrays −

Example

In the following example, we are declaring an array, assigning values to the array, and then accessing array elements −

 #include <iostream> using namespace std; #include <iomanip> using std::setw; int main () { int n[ 10 ]; // n is an array of 10 integers // initialize elements of array n to 0 for ( int i = 0; i < 10; i++ ) { n[ i ] = i + 100; // set element at location i to i + 100 } cout << "Element" << setw( 13 ) << "Value" << endl; // output each array element's value for ( int j = 0; j < 10; j++ ) { cout << setw( 7 )<< j << setw( 13 ) << n[ j ] << endl; } return 0; } 

This program makes use of setw() function to format the output. When the above code is compiled and executed, it produces the following result −

Output

 Element Value 0 100 1 101 2 102 3 103 4 104 5 105 6 106 7 107 8 108 9 109 

Getting Array Length

To get the length of an array, you can use the sizeof() operator by dividing the size of the array with the size of the array elements.

Consider the following syntax −

 length = sizeof(arr) / sizeof(arr[0]); 

Example

In the following example, we are defining an array and finding it's length −

 #include <iostream> using namespace std; int main() { int arr[] = {10, 20, 30, 40, 50}; int arr_length = sizeof(arr) / sizeof(arr[0]); cout << "Array's Length : " << arr_length; return 0; } 

Output

 Array's Length : 5 

Changing Array Element

You can change the value of an array element by specifying its index and assigning a new value.

Example

In the following example, we are changing the value at index 2 −

 #include <iostream> using namespace std; int main() { int arr[] = {10, 20, 30, 40, 50}; cout << "Before changing, element at index 2: " << arr[2] << endl; // changing the value arr[2] = 108; cout << "After changing, element at index 2: " << arr[2] << endl; return 0; } 

Output

 Before changing, element at index 2: 30 After changing, element at index 2: 108 

More on C++ Arrays

Arrays are important to C++ and should need lots of more detail. There are following few important concepts, which should be clear to a C++ programmer −