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C++ Exercises: Check if a number is Keith or not

C++ Numbers: Exercise-40 with Solution

Write a program in C++ to check if a number is Keith or not.

Sample Solution:

C++ Code :

#include<bits/stdc++.h>
using namespace std;

int lenCount(int nm)
{  int ctr=0;
    while(nm>0)
    {
        nm=nm/10;
        ctr++;
     }
     return ctr; 
}

int main()
{
    int num1=0,arr1[10],num2=0,flg=0,i=0,sum=0;
	cout << "\n\n Check whether a number is Keith or not: \n";
	cout <<" Sample Keith numbers: 197, 742, 1104, 1537, 2208, 2580, 3684, 4788, 7385..\n";
	cout << " -----------------------------------------------------------------------\n";	
	cout<<" Input a number : ";
    cin>>num1;
    num2=num1;
    for(i=lenCount(num2)-1;i>=0;i--)
    {
        arr1[i]=num1 % 10;
        num1/=10;
    }
    while(flg==0)
    {
        for(i=0;i<lenCount(num2);i++)
            sum+=arr1[i];
        if(sum==num2)
        {
            cout<<" The given number is a Keith Number.\n";
            flg=1;
        }
        if(sum>num2)
        {
            cout<<" The given number is not a Keith number.\n";
            flg=1;
        }
        for(i=0;i<lenCount(num2);i++)
        {
            if(i!=lenCount(num2)-1)
                arr1[i]=arr1[i+1];
            else
                arr1[i]=sum;
        }
        sum=0;
    }
}

Sample Output:

 Check whether a number is Keith or not:                               
 Sample Keith numbers: 197, 742, 1104, 1537, 2208, 2580, 3684, 4788, 7385..                                                                   
 -----------------------------------------------------------------------                                                                     
 Input a number : 742                                                  
 The given number is a Keith Number.

Flowchart:

Flowchart: Check if a number is Keith or not

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