﻿ C++ Exercises: Create the first twenty Hamming numbers - w3resource

# C++ Exercises: Create the first twenty Hamming numbers

## C++ Numbers: Exercise-42 with Solution

Write a program in C++ to create the first twenty Hamming numbers.

Sample Solution:

C++ Code:

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

bool chkHhamming (int n)
{
if (n == 1) return true;
if (n%2==0 or n%3==0 or n%5==0)
{
for (int i = 2; i*i < n; ++i)
{
if (n%i == 0) {
if (i%2 != 0 and i%3!=0 and

i%5!=0) return false;
}
if (n%(n/i) == 0) {
if ((n/i)%2 != 0 and (n/i)%3!=0

and (n/i)%5!=0) return false;
}
}
return true;
}
return false;
}

int main ()
{
int n,j;
cout << "\n\n Find first twenty Hamming numbers: \n";
cout << " ---------------------------------------\n";
cout << " Input the upper limit of Hamming numbers: ";
cin>>n;
cout << " The Hamming numbers are: "<<endl;

while (j<=n)
{
int count = 0;
int i = 1;
bool first = true;
while (count < n)
{
if (chkHhamming(i))
{
if (not first) cout << ",";
cout << i;
++count;
first = false;
}
++i;
}
j++;
}
cout <<endl;
}
``````

Sample Output:

``` Find first twenty Hamming numbers:
---------------------------------------
Input the upper limit of Hamming numbers: 20
The Hamming numbers are:
1,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,1
2,15,16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,
27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30,32,361,2,3,4,5
,6,8,9,10,12,15,16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,1
8,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30,32,
361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10
,12,15,16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,2
5,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30,32,361,2,3,4
,5,6,8,9,10,12,15,16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16
,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30,3
2,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,
10,12,15,16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24
,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30,32,361,2,3
,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,
16,18,20,24,25,27,30,32,361,2,3,4,5,6,8,9,10,12,15,16,18,20,24,25,27,30
,32,36
```

Flowchart:

C++ Code Editor:

What is the difficulty level of this exercise?

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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