﻿ C++ Exercises: Display the first 10 Lucus numbers - w3resource

# C++ Exercises: Display the first 10 Lucus numbers

## C++ Numbers: Exercise-14 with Solution

Write a program in C++ to display the first 10 Lucus numbers.

Pictorial Presentation:

Sample Solution:

C++ Code :

``````#include <iostream>
#include <cmath>
using namespace std;
int main()
{
cout << "\n\n Find the first 10 Lucus numbers: \n";
cout << " -------------------------------------\n";
cout << " The first 10 Lucus numbers are: "<<endl;

int n = 10;
int n1 = 2, n2 = 1, n3;
if (n > 1)
{
cout<<n1<<" "<<n2<<" ";
for(int i = 2; i < n; ++i)
{
n3 = n2;
n2 += n1;
n1 = n3;
cout<< n2 <<" ";
}
cout<<endl;
}
else if (n == 1)
{
cout<<n2<<" ";
cout<<endl;
}
else
{
cout<<"Input a positive number."<<endl;
}
}
``````

Sample Output:

```Find the first 10 Lucus numbers:
-------------------------------------
The first 10 Lucus numbers are:
2 1 3 4 7 11 18 29 47 76
```

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