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

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

## C++ Numbers: Exercise-15 with Solution

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

Pictorial Presentation:

Sample Solution:

C++ Code :

``````#include<iostream>
using namespace std;
unsigned long int cataLan(unsigned int n)
{
if (n <= 1) return 1;
unsigned long int catno = 0;
for (int i=0; i<n; i++)
catno += cataLan(i)*cataLan(n-i-1);
return catno;
}
int main()
{
cout << "\n\n Find the first 10 Catlan numbers: \n";
cout << " --------------------------------------\n";
cout << " The first 10 Catlan numbers are: "<<endl;
for (int i=0; i<10; i++)
cout << cataLan(i) << " ";
cout <<endl;
return 0;
}
``````

Sample Output:

``` Find the first 10 Catlan numbers:
--------------------------------------
The first 10 Catlan numbers are:
1 1 2 5 14 42 132 429 1430 4862
```

Flowchart:

C++ Code Editor:

What is the difficulty level of this exercise?

﻿

## 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