~cpp 
#include <iostream.h>
#include <math.h>
#include <time.h>

int main()
{
	int tmp_arr[10000]={2,0};
	int cur_arr_index = 1;
	int i,j;
	bool flag;

	clock_t t = clock();
	

	for(i=3; i<50000; i++)	{
		flag = true;
		for(j=0; tmp_arr[j]<=sqrt(i); j++)
		//for(j=0; j<cur_arr_index; j++)
		{
			if(i%tmp_arr[j]==0)	{
				flag=false;
				break;
			}
			else continue;
		}
		if(flag) tmp_arr[cur_arr_index++]=i; 
	}

	/*double ti = clock()-t;
	double clk = CLOCKS_PER_SEC;
	cout << ti/clk << endl;*/

	/*for(i=0; i<cur_arr_index; i++)
		cout << tmp_arr[i] << ' ';*/

	
	double ti = clock()-t;
	double clk = CLOCKS_PER_SEC;
	cout << ti/clk << endl;

	return 0;
}
 

~cpp 
  for(j=0; tmp_arr[j]<sqrt(i); j++) 

~cpp 
    for(j=0; tmp_arr[j]<=sqrt(i); j++)