PRACTICE PROBLEMS 2 (24-1 to 31-1) : CIRCULAR PRIMES

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For a detailed explaination :VIDEO HERE
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#include<stdio.h>
#include<math.h>
int len(int);
int prime(int);
void main()
{
int N;
int i;
scanf("%d",&N);
int r=len(N);
int p=0;
for(i=1;i<=r;i++)
{
int num=N;
int j;
int le=len(N);
for(j=0;j<i;j++)
{
int rem=num%10;
num=(num/10)+(rem*pow(10,le-1));
}
int result=prime(num);
if(result==1)
p++;
}
if(p==r)
printf("Circular prime");
else
printf("Not circular prime");
}
int len(int a)
{
int l=0;
while(a>0)
{
l++;
a/=10;
}
return l;
}
int prime(int n)
{
int c=1;
int i;
for(i=2;i<n;i++)
{
if(n%i==0)
{
c=0;
break;
}
}
return c;
}