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Arrays in C++


August 27, 2022, Learn eTutorial
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In this tutorial, you will learn everything about the data structure called an array. With the help of simple examples, you will understand how to declare, initialize and access variables from arrays.

An array is a variable in C++ that can hold multiple values of the same type. 

For example,

Assume we have 29 students in a class and we need to save their grades. Instead of making 29 individual variables, we can simply make an array:


double grade[29];
 

Here in the above example, the grade is an array with a maximum capacity of 29 double-type elements.

Arrays in C++ cannot be changed after they have been declared.

What do you mean by an array?

  • It is a collection of variables with similar data types that are referred to by a single element.
  • Its components are kept in a single, continuous memory location.
  • The array's size should be specified when it is declared.
  • Array elements are always counted beginning with zero (0).
  • The position of an array element in the array can be used to access it.
  • There can be one or more dimensions in the array.

In C/C++ or any other programming language, an array is a group of related data items stored at adjacent memory locations, and its elements can be accessed at random using an array's indices.  They can be used to store any type of primitive data type, such as int, float, double, char, and so on. Furthermore, in C/C++, an array is primarily used to store derived data types such as structures, pointers, and so on. 

A pictorial representation of an array is given below.
 

Arrays in C++

How to declare an array in C++?

The general syntax of defining array is like-

dataType arrayName[arraySize];

See the below example :

int x[6];

In the above example

  • int = It refers to the type of element that will be stored.
  • x = it refers to the name of the array
  • 6 = it refers to the array size

In this case array, x[6] creates six adjacent cells in memory which are x[0], x[1], sal[2], x[3], x[4], and x[5] for storing the int type values.

The allocation of arrays starts with a 'null' and consequently the last variable of the series will be stored at x[size -1]. In our example, the first element of the array will be allocated at x[0] and the last element will be allotted at x[5].

How to access array elements in C++?

Each element in an array is assigned a number in C++. The number is referred to as an array index. Using those indices, we can access array elements.

Syntax in order  to access array elements

array[index];
Arrays in C++

This fig shows the elements of an array in C++

Remember the following:

  • The array indexes begin with 0. x[0] denotes the first element stored at index 0.
  • If an array has n elements, the last element is stored at index (n-1). The last element in this example is x[5].
  • An array's elements have consecutive addresses. Assume that the starting address of x[0] is 2120.
  • The address of the next element x[1] will then be 2124, x[2] will be 2128, and so on.
  • Each element's size is increased by four in this case. This is due to the fact that int has a size of 4 bytes.

Array Initialization in C++

Array initialization is a process of assigning values to the array elements. Array elements must be initialized before they can be used in the program. If they are not properly initialized the program produces unexpected results. Let us understand how arrays are initialized using examples.

It is possible to initialize an array during declaration in C++. 

For example: let us declare and initialize  an array

int x[6] = {10, 20, 30, 40, 50, 60};
Arrays in C++

This fig shows the C++ array elements and their data

Another way to initialize an array during its declaration:

int x[] = {10, 20, 30, 40, 50, 60};

We haven't mentioned the array's size here. In such cases, the compiler computes the size automatically.

We can initialize the array after declaration. Let's take an example

int x[3];
x[0] = 10;
x[1] = 20;
x[2] = 30;

An array With Empty Members in C++

An array with no members means empty members.  In C++, if an array has a size of n, we can store up to n elements in it. However, in C++ what happens if we store fewer than n elements? 

For example


//let us store only 3 elements in the array
int x[6] = {10, 20, 30};

The array x has a size of 6 in this case. However, we've only given it three elements, to begin with.

The compiler assigns random values to the remaining places in such cases. Frequently, this random value is just 0. The empty array members are assigned 0 automatically.

An array With Empty Members in C++

Displaying the array elements in C++

We utilize cout function to print the values accessed from an array using their indices with the help of loops.

Example 1 : How to print array elements using for loop.


#include 
using namespace std;

int main() {

  int numbers[5] = {10, 20, 30, 40, 50};

  cout << "The numbers : ";

  //  Printing the array elements
  // using the range based for loop
    for (int i = 0; i < 5; ++i) {
    cout << numbers[i] << "  ";
  }

  return 0;
}

Output:

The numbers : 10  20  30  40  50 

In this example for loop was used to iterate from i = 0 to i = 4. We have printed numbers[i] in each iteration.

Let's discuss how to display array elements using range-based loop:

Example 1 : How to print an array elements using for loop.


#include 
using namespace std;

int main() {

  int numbers[5] = {10, 20, 30, 40, 50};

  cout << "The numbers : ";

  //  Printing the array elements
  // using the range based for loop
  for (const int &n : numbers) {
    cout << n << "  ";
  }

  return 0;
}

Output:

The numbers : 10  20  30  40  50 

In our range-based loop, we used const int &n as the range declaration instead of int n. The const int &n, on the other hand, is better preferred because:

  • Each iteration of int n simply copies the array elements to the variable n. Memory usage is not effective in this.
  • &n, on the other hand, uses the array elements' memory addresses to access their data without copying it to a new variable. This is memory-saving.
  • We're just printing the array elements, not changing them. As a result, we use const to avoid accidentally changing the array's values.

To learn more about this Ranged Loop, check C++ Ranged for Loop.

How to insert array elements in C++?

With the help of the cin function and loops, we can input values into an array. 

Let us write a C++ program that will take the inputs from the user and will be stored in an array.


#include <iostream>
using namespace std;

int main() {

  int numbers[5];

  cout << " please enter 5 numbers: " << endl;

  //  store the  input from user to an array
  for (int i = 0; i < 5; ++i) {
    cin >> numbers[i];
  }

  cout << " So the numbers are: ";

  //  print the array elements
  for (int n = 0; n < 5; ++n) {
    cout << numbers[n] << "  ";
  }

  return 0;
}

Output:

please enter 5 numbers: 
11
12
17
18
19
So the numbers are: 11  12  17  18  19  

We used a for loop once more to iterate from i = 0 to i = 4. In each iteration, we took a user input and stored it in numbers[i].

We then used another for loop to print out all of the array elements.

Using for Loop, display the sum and average of array elements in C++

#include <iostream>
using namespace std;

int main() {
    
  // first initialize an array without specifying its  size
  double numbers[] = {7, 15, 16, 12, 35, 2};

  double sum = 0;
  double count = 0;
  double average;

  cout << "So the numbers are: ";

  //  print the array elements
  // here, use of range-based for loop
  for (const double &n : numbers) {
    cout << n << "  ";

    //  calculate the sum
    sum += n;

    // count the number of the array elements
    ++count;
  }

  // print the sum
  cout << "\nTheir Sum = " << sum << endl;

  // find the average
  average = sum / count;
  cout << "Their Average = " << average << endl;

  return 0;
}

Output:

So the numbers are: 7  15  16  12  35  2  
Their Sum = 87
Their Average = 14.5

In the program :

  • We created a double array called numbers but did not specify its size. In addition, three double variables were declared: sum, count, and average.
  • In this case, sum = 0 and count = 0.
  • The array elements were then printed using a range-based for loop. In each loop iteration, we added the current array element to sum.
  • In order to know the size of the array at the conclusion of the for loop, we also raise the value of count by 1 with each iteration.
  • We print the sum and average of all the numbers after printing all of the elements. Average = sum / count gives the average of the numbers.

Note:

Here in this program, a ranged for loop was used in place of a normal for loop.

The size of the array determines the number of iterations in a normal for loop, which must be specified.

A ranged for loop, on the other hand, does not require such kind of specifications.

What is an array out of bounds in C++?

If we declare a 10-element array, the array will contain elements from 0 to 9.
However, attempting to access the element at index 10 or higher will result in Undefined Behaviour. This is what is known as the array out of bounds in C++.

Why do we require arrays?

When we have a small number of objects, then we can use normal variables (v1, v2, v3, etc.), but when we have a very large number of instances, it will become very difficult in order to manage them with the normal variables. So the main idea behind the usage of an array is to represent multiple instances in a single variable.

Arrays in C++

Advantage of arrays

  • The code optimization, as well as the random access, are the main advantage of an array.
  • Code optimization: We can efficiently retrieve or sort the data.
  • Random Access: We can retrieve any data that is located at an index position.

Disadvantage

  • The size limit of an array is the main disadvantage of an array
  • Size limit : Only elements with fixed sizes can be stored in an array. It doesn't enlarge in size while running.

 To practice more programs in arrays refer to our sample programs.