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Fascinating Number Program in C

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In this tutorial, we will write a C program to check whether the given number is a Fascinating number or not. You may go through the following topics first in C.

What is Fascinating Number?

A number is said to be a fascinating number if it is (having at least 3 digits) multiplied by 2 and 3, and then both these product’s results are concatenated with the original number, then the new number contains all the digits from 1 to 9 exactly once. There could be any number of zeros and are ignored.

Fascinating number example:

Consider a Number = 192
Then multiply it by two and 3
192 × 2 = 384
192 × 3 = 576
Concatenating the above two numbers with the original number, we get:
“192” + “384” + “576” = 192384576 = result.
Now the final result contains all the digits from 1 to 9. Hence it is a Fascinating Number.

Procedure for Fascinating Number

  1. First, check if the entered/given number has three digits or not. If not, print “cannot be a Fascinating Number”.
  2. Else, Multiply the given number with 2 and 3.
  3. Then convert the product result into a string and Concatenate those strings along with the original number.
  4. Iterate the string that we get after concatenation and also keep the frequency count of the digits.
  5. Print “Not a Fascinating Number” if any of the digits (1 to 9) is missing or repeated.
  6. Else, print “It is a Fascinating Number”.

C Program for Fascinating Number

#include <stdio.h>
#include <stdbool.h>
#include <math.h>

//function
int countDigits(int n)
{
  int count = 0;
  while (n > 0)
  {
    count++;
    n /= 10;
  }

  return count;
}

int main(void)
{
  int num;

  printf("Enter a number: ");
  scanf("%d", &num);

  //calculating the product
  int product2 = num * 2;
  int product3 = num * 3;

  //Concatinating all three
  int concatNum = 0;
  concatNum += num;
  concatNum = concatNum* pow(10, countDigits(product2)) + product2;
  concatNum = concatNum* pow(10, countDigits(product3)) + product3;

  //Count the occurence
  int count[10] = { 0 };
  while (concatNum > 0)
  {
    count[concatNum % 10]++;
    concatNum = concatNum / 10;
  }

  //Check for 1
  bool isFound = true;
  for (int i = 1; i < 10; i++)
  {
    if (count[i] != 1)
    {
      isFound = false;
      break;
    }
  }

  //Display the result
  if (isFound)
    printf("%d is a Fascinating number.", num);
  else
    printf("%d is NOT a Fascinating number.", num);

  return 0;
}

Output:

Enter a number: 192
192 is a Fascinating number.

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