﻿ C++ : Find Lychrel number within the range 1 to 1000

# C++ Exercises: Find the Lychrel numbers and the number of Lychrel number within the range 1 to 1000

## C++ Numbers: Exercise-12 with Solution

Write a program in C++ to find the Lychrel numbers and the number of Lychrel number within the range 1 to 1000 (after 500 iteration).

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,ctr=0,i;
bool l;
cout << "\n\n Find the Lychrel numbers between 1 to 1000(after 500 iteration): \n";
cout << " ----------------------------------------------------------------------\n";
cout << " The Lychrel numbers are : ";
for (i=1;i<=1000;i++)
{
lyno=i;
l = isLychrel(lyno);
if(l==1)
{
ctr++;
cout<<lyno<<" ";
}}
cout<<endl;
cout <<" The number of Lychrel numbers are: "<<ctr<<endl;
return 0;

}
``````

Sample Output:

```Find the Lychrel numbers between 1 to 1000(after 500 iteration):
----------------------------------------------------------------------
The Lychrel numbers are : 196 295 394 493 592 689 691 788 790 879 887 978 986
The number of Lychrel numbers are: 13
```

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