NOIP 2007年信息学奥赛初赛普及组阅读程序写结果：
#include "math.h"
#include "stdio.h"
main()
{
int a1[51] = { 0 };
int i, j, t, t2, n = 50;
for ( i = 2; i <= sqrt( n ); i++ )
if ( a1[i] == 0 )
{
t2 = n / i;
for ( j = 2; j <= t2; j++ )
a1[i * j] = 1;
}
t = 0;
for ( i = 2; i <= n; i++ )
if ( a1[i] == 0 )
{
printf( "%4d", i );
t++;
if ( t % 10 == 0 )
printf( "\n" );
}
printf( "\n" );
}输出: ___
___