1.　　编写筛选查找素数函数：

void sieve(bool isPrime[], int n)

其中isPrime[n]为一个布尔型数组，n为数组大小。由于2是第一个素数，所以设置isPrime[0]和isPrime[1]的值为false，并设置其余的元素初值为true。然后对从4到n－1的每一个i，判断i是否能够被2整除，如果i能够被2整除，则设置isPrime[i]为false。对从2到n/2的每一个可能的数值重复以上处理，当操作结束时，所有值为true的isPrime[i]所对应的i就是素数，它们将是从筛子中掉下来的。

测试程序：

输入：一个整数,表示n

输出：1行，1到n之间的所有素数，两个素数之间用空格隔开，最后一个素数输出后，输出一个空格和空行，输出参见函数Disp的代码。

例如，当输入20时，输出如下：

2 3 5 7 11 13 17 19

-1. Preparation of screening to find primes function: void sieve (bool isPrime [], int n) where isPrime [n] is a Boolean array, n is the array size. Because 2 is the first prime number, so set isPrime [0] and isPrime [1] the value is false, and set the rest of the elements of the initial value to true. Then　4 to n-1 every i, i determine whether it can be divisible by 2, if i can be divisible by 2, set isPrime [i] is false. For every possible value　2 to n/2 Repeat the above process, when the end of the operation, all the value of true isPrime [i] corresponding to the i is a prime number, they will be falling　the sieve come. Test Procedure: Input: An integer representing the n output: 1 line, all the prime numbers between 1 and n, separated by a space between two prime number, a prime number after the last output, the output of a blank and blank lines, see the output function Disp code. For example, when the input 20, the output is as follows: 235711131719