Initialization of a normal array with one default value in C++

An array is a fixed-size collection of elements of the same data type that stores data in contiguous memory locations. Initializing an array with one default value in C++ is an easy task and can be easily implemented using various approaches that we are going to understand with code examples.

Initializing Array with Zeroes in C++

To initialize all elements of an array with 0, we will simply initialize the array with 0 or just use empty curly braces.

Example

Here is an example that uses the above mentioned methods to initialize the array with 0:

#include <iostream>
using namespace std;
int main()
{
   int a[10] = {0};
   int d[10] = {};
   cout << "Elements of array a: ";
   for (int i = 0; i < 10; i++)
   {
      cout << a[i] << " ";
   }
   cout << "\n";
   cout << "Elements of array d: ";
   for (int i = 0; i < 10; i++)
   {
      cout << d[i] << " ";
   }
}

The output of the above code is as follows:

Elements of array a: 0 0 0 0 0 0 0 0 0 0 
Elements of array d: 0 0 0 0 0 0 0 0 0 0

Here is a list of approaches to initialize an array with one default value:

• Using for Loop
• Using array::fill() Function
• Using vector

Using for Loop

The following approach uses the for loop to initialize all elements with a specific value. We have used two arrays: arr and arr2.

• The first array arr uses arr[10] = {5} to initialize all elements with 5, but here only the first element is set to 5, and the rest are 0.
• The second array arr2, uses a for loop to iterate over all the elements starting from 0th index to end of the array (n-1) and setting each element to specific value.

Example

The following example initializes all array elements of arr2 to 5 using for loop:

#include <iostream>
using namespace std;
int main()
{
   
   int arr[10] = {5};
   cout << "Elements of array arr: ";
   for (int i = 0; i < 10; i++)
   {
      cout << arr[i] << " ";
   }
   cout << "\n";

   int arr2[10];   
   cout << "Elements of array arr2: ";
   for (int i = 0; i < 10; i++)
   {
      arr2[i] = 5;   // Initializing array elements to 5
      cout << arr2[i] << " ";    // Displaying array elements
   }
   cout << "\n";
   return 0;
}

The output of the above code is as follows:

Elements of array arr: 5 0 0 0 0 0 0 0 0 0 
Elements of array arr2: 5 5 5 5 5 5 5 5 5 5

Using array::fill() Function

The array::fill() function assigns a specific value to all elements of an array.

Example

The following example uses the array::fill() function to set all elements of the array to 5:

#include <iostream>
#include <array>
using namespace std;

int main()
{
   array<int, 10> arr;
   arr.fill(5);

   cout << "Elements of Array arr: ";
   for (int i = 0; i < 10; ++i)
   {
      cout << arr[i] << " ";
   }
}

The output of the above code is as follows:

Elements of Array arr: 5 5 5 5 5 5 5 5 5 5

Using vector

To initialize an array with one default value, we have used vector. It will create an object v and it uses constructor v(10, 5) that creates a vector array of 10 elements and initialize each element to 5.

Example

Here is an example using vector to initialize all the array elements with 5:

#include <iostream>
#include <vector>
using namespace std;

int main()
{
   // Array of 10 elements, each element is 5
   vector<int> v(10, 5);    
   
   cout << "Elements of Array v: ";
   for (int i = 0; i < 10; ++i)
   {
      cout << v[i] << " ";
   }
}

The output of the above code is as follows:

Elements of Array v: 5 5 5 5 5 5 5 5 5 5