﻿ C++ Exercises: Check whether a number is Lychrel number or not - w3resource

# C++ Exercises: Check whether a number is Lychrel number or not

## C++ Numbers: Exercise-11 with Solution

Write a program in C++ to check whether a number is Lychrel number or not.

Pictorial Presentation:

Sample Solution:

C++ Code :

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

long long int numReverse(long long int number)
{
long long int rem = 0;
while (number > 0)
{
rem = (rem * 10) + (number % 10);
number = number / 10;
}
return rem;
}
bool is_Palindrome(long long int num)
{
return (num == numReverse(num));
}
bool isLychrel(int num, const int iterCount = 500)
{
long long int temp = num;
long long int rev;
for (int i = 0; i < iterCount; i++)
{
rev = numReverse(temp);
if (is_Palindrome(rev + temp))
return false;
temp = temp + rev;
}
return true;
}
int main()
{
int lyno;
bool l;
cout << "\n\n Check whether a given number is a Lychrel number: \n";
cout << " ------------------------------------------------------\n";
cout << " Input a number: ";
cin >> lyno;
l = isLychrel(lyno);
if (l==0)
{
cout <<" The number is not a Lychrel number."<<endl;
}
else
if(l==1)
{
cout<<" The number is a Lychrel number."<<endl;;
}
return 0;
}
``````

Sample Output:

```Check whether a given number is a Lychrel number:
------------------------------------------------------
Input a number: 196
The number is a Lychrel number.
```

Flowchart:

C++ Code Editor:

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## C++ Programming: Tips of the Day

How to use the PI constant in C++?

On some (especially older) platforms (see the comments below) you might need to

#define _USE_MATH_DEFINES and then include the necessary header file:
`#include<math.h>`

and the value of pi can be accessed via:

`M_PI`

In math.h (2014) it is defined as:

`# define M_PI           3.14159265358979323846  /* pi */`

but check your math.h for more. An extract from the "old" math.h (in 2009):

```/* Define _USE_MATH_DEFINES before including math.h to expose these macro
* definitions for common math constants.  These are placed under an #ifdef
* since these commonly-defined names are not part of the C/C++ standards.
*/```

However:

1. on newer platforms (at least on my 64 bit Ubuntu 14.04) I do not need to define the _USE_MATH_DEFINES
2. On (recent) Linux platforms there are long double values too provided as a GNU Extension:
`# define M_PIl          3.14159265358979323846`

Ref: https://bit.ly/3G4BgzQ