In this tutorial, we will write a neon number program in Cpp. We will write two different programs.
- Check for neon number
- Display the neon number within the range
Neon Numbers
A number is said to be a neon number if the sum of the digits of a square of the number is equal t the original number.
Example: 9 is a Neon number (see explanation in the diagram).

Neon Number in C++
C++ Program to check for neon numbers.
//Cpp Program to check whether a given number is a Neon number or not
#include <iostream>
using namespace std;
int main()
{
int num;
cout << "Enter the number: ";
cin >> num;
int square = num * num;
int sum = 0;
while (square > 0)
{
int lastDigit = square % 10;
sum = sum + lastDigit;
square = square / 10;
}
if (sum == num)
cout << num << " is a Neon number";
else
cout << num << " is NOT a Neon number";
return 0;
}
Output:
Enter the number: 9
9 is a Neon number
C++ program to display all the neon number within a given range
//Cpp Program to check whether a given number is a Neon number or not
#include <iostream>
using namespace std;
int checkForNeon(int x)
{
int square = x * x;
int sumOfDigits = 0;
while (square != 0)
{
sumOfDigits = sumOfDigits + square % 10;
square /= 10;
}
return (sumOfDigits == x);
}
// Main function
int main(void)
{
int lowestNum, highestNum;
cout << "ENTER THE STARTING AND FINAL NUMBER FOR THE RANGE TO CHECK\n";
cout << "\nEnter the lowest number: ";
cin >> lowestNum;
cout << "Enter the Highest number: ";
cin >> highestNum;
cout << "\nNeon Number between them are:";
for (int i = lowestNum; i <= highestNum; i++)
{
if (checkForNeon(i))
cout << i << " ";
}
}
Output:
ENTER THE STARTING AND FINAL NUMBER FOR THE RANGE TO CHECK
Enter the lowest number: 1
Enter the Highest number: 2000
Neon Number between them are:1 9