质数（prime number）又称素数，有无限个。质数定义为在大于1的自然数中，除了1和它本身以外不再有其他因数的数称为质数。-- 来自“百度百科”
#include <iostream>
#include <iomanip>
using std::cout;
using std::cin;
using std::endl;
int main()
{
int max = 0;
int count = 3;
long trial = 5;
bool isprime = true;
cout << endl
<< "Enter the number of primes you would like: ";
cin >> max;
long* primes = new long[max];
*primes = 2;
*(primes + 1) = 3;
*(primes + 2) = 5;
do {
trial += 2;
int i = 0;
cout << "trial is " << trial << endl;
do {
isprime = trial % *(primes + i) > 0;
cout << "+++ trial is " << trial << " and i is " << i << " prime is " << *(primes + i) << endl;
} while (++i < count && isprime);
if (isprime) {
*(primes + count++) = trial;
cout << "add trial = " << trial << endl;
} else {
cout << "do not add trial = " << trial << endl;
}
} while (count < max);
for (int i = 0; i < max; i++) {
if (i % 5 == 0) {
cout << endl;
}
cout << std::setw(10) << *(primes + i);
}
cout << endl;
delete [] primes;
primes = 0;
return 0;
}
编译并运行，测试生成五个的输出如下：
➜ C g++ hello.cpp
➜ C ./a.out
Enter the number of primes you would like: 5
trial is 7
+++ trial is 7 and i is 0 prime is 2
+++ trial is 7 and i is 1 prime is 3
+++ trial is 7 and i is 2 prime is 5
add trial = 7
trial is 9
+++ trial is 9 and i is 0 prime is 2
+++ trial is 9 and i is 1 prime is 3
do not add trial = 9
trial is 11
+++ trial is 11 and i is 0 prime is 2
+++ trial is 11 and i is 1 prime is 3
+++ trial is 11 and i is 2 prime is 5
+++ trial is 11 and i is 3 prime is 7
add trial = 11
2 3 5 7 11
从输出来看，大体的意思就是，首先看奇数，然后再挨个看能否被之前的质数整除，都不行的话，那就是新的质数。
- 例子代码参考自《C++入门经典》
