﻿ C++ : Check if a given number is circular prime or not

# C++ Exercises: Check if a given number is circular prime or not

## C++ Numbers: Exercise-30 with Solution

Write a program in C++ to check if a given number is circular prime or not.

Sample Solution:

C++ Code :

``````#include<iostream>
#include<cmath>
using namespace std;
int flg;
void chkPrime(long int n)
{
long int i;
i=n-1;
while(i>=2)
{
if(n%i==0)
{
flg=1;
}
i--;
}
}
void AllCombination(long int a)
{
long int b1,c1,d1,e1,i,j,k,s1,z1,v1,x[8],y[8],m;
b1=a;
i=0;
while(b1>0)
{
y[i]=b1 % 10;
b1=b1/10;
i++;
}
c1=0;
for(j=i-1;j>=0;j--)
{
x[c1]=y[j];
c1++;
}
m=i;
while(m>0)
{
c1=m-1;
d1=i-1;
e1=0;
s1=0;
while(e1<i)
{
z1=pow(10,d1);
v1=z1*x[c1%i];
c1++;
d1--;
e1++;
s1=s1+v1;
}
m--;
chkPrime(s1);
}
}
int main()
{
long int num1;
cout << "\n\n Check whether a given number is circular prime or not: \n";
cout << " -----------------------------------------------------------\n";
cout<<" Input a Number: ";
cin>>num1;
flg=0;
AllCombination(num1);
if(flg==0)
{
cout << " The given number is a circular prime Number."<<endl;
}
else
{
cout << " The given number is not a circular prime Number."<<endl;
}
return 0;
cout<<endl;
}
``````

Sample Output:

```Check whether a given number is circular prime or not:
-----------------------------------------------------------
Input a Number: 11
The given number is a circular prime Number
```

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