C++ program to find index of an array element

In this blog, we will create a program to find an index of an element by element value.

Index of an element?

Lists are an ordered collection of items, each element has its own unique position, and each element can be accessed by telling Python the position. These positions are called indexes.

Algorithm to find an index of an element

  • First, create the index of the local variable.
  • Initialize the index with -1.
  • Go through the entire field:
  • If the current value is equal to the given value, replace the index value.
  • Break the loop.
  • Print the index value

C++ code to find an index of an element

// C++ program to find index of an element
#include <iostream>
using namespace std;
// Driver Code
int main()
{
int arr[] = {12, 56, 823, 7, 1023};
// n is the size of array 
int n = sizeof(arr) / sizeof(arr[0]);
//Intialize the value of index
int index = -1;
// Let's suppose we have to find index of 56
int element = 56;
// Iterate the array
for(int i=0;i<n;i++)
{
if(arr[i]==element)
{
//If current value is equal to our element then replace the index value and break the loop
index = i;
break;
}
}
if(index==-1)
{
cout<<"Element doesn't exist in array" <<endl;
}
else
{
cout << "Index of " << element<<" is "<< index << endl;
}
return 0;
}

The output of the above code

Let’s take another example where an element doesn’t exist

// C++ program to find index of an element
#include <iostream>
using namespace std;
// Driver Code
int main()
{
    int arr[] = {12, 56, 823, 7, 1023};
    // n is the size of array 
    int n = sizeof(arr) / sizeof(arr[0]);
    //Intialize the value of index
    int index = -1;
    // Let's suppose we have to find index of 55
    int element = 55;
    // Iterate the array
    for(int i=0;i<n;i++)
    {
        if(arr[i]==element)
        {
            //If current value is equal to our element then replace the index value and break the loop
            index = i;
            break;
        }
    }
    if(index == -1)
    {
        cout<<"Element doesn't exist in array" <<endl;
    }
    else
    {
        cout << "Index of " << element<<" is "<< index << endl;
    }
    return 0;
}

The output of the above code

Explanation of the code

If the element in the array does not exist, then the find() function returns the last iterator or the address of the element next to the last in the array. We subtracted it with the address of the array’s first element and returned a number greater than the array’s size. This proved that the element did not exist in the array.