Miscellany

#include <stdio.h>
#include <time.h>
#define N 100

time_t start,finish;
int    isprime(int );
int    k,init_prime,next_prime,run,number,in_pr=0;
double duration;

main()
{

  start=time(0);
  init_prime=3;  // oi 2 prwtoi pou anamesa tous vriskontai oi sunthetoi
  next_prime=0;
  
run=init_prime+2;
number=0;
k=1;
while(k<N)
 {
  if (isprime(run))
  {
    next_prime=run;                  //vriskw ton next_prime
    number=next_prime-init_prime-1;  //to plhthos twn sunthetwn
    in_pr=init_prime;
    init_prime=next_prime;
    if (number==k)
    {
       printf("First %d consecutive composites from %d to %d\n",k,in_pr+1,next_prime-1);   //an einai o epithumhtos ton emfanizw
       init_prime=3;
       run=init_prime;
       next_prime=0;
       k+=2;
    }    
   
   } 

   run+=2;

 }
finish=time(0);
duration=difftime(finish,start);
printf("Program was executed in %lf seconds\n",duration);
}



//sunarthsh isprime()..elegxei an enas arithmos>2 einai prwtos


int isprime(int run)
{
 int i=2;
 int done=1;
 while (done==1 && i*i<run) 
  {
     if (run % i==0)
     {
       done=0;
       break;
     }

     i++;
  }
  return done;
}