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法律研究使用轮式筛法生成给定范围内的素数的 C++ 程序
轮筛法用于寻找给定范围内的素数。轮式分解是一种手动执行埃拉托斯特尼筛法以将素数与合数分开的图形方法，即筛选法。
在此方法中，内圆内的素数在其与其他圆内的位置上具有其倍数，形成素数和其倍数的辐条。内圆中这些素数的倍数形成外圆中合数的辐条。
算法
Begin Define max number gen_sieve_primes() Declare c Assign c = 2 For p = 2 to max number If prime[p]==0 prime[p]=1 Mul = p multiply c For Mul less than max number prime[Mul] = -1 Increment c Mul = p multiply c Done Done Print_all_prime() Assign c=0 For i = 0 to max number if (prime[i] == 1) Increment c If c less than 4 Switch(c) Case 1 Print 1st prime number Case 2 Print 2nd prime number Case 3 Print 3rd prime number Else Print nth prime number End
示例代码
#include <iostream>
using namespace std;
#define MAX_NUMBER 40
int prime[MAX_NUMBER];
void gen_sieve_prime(void) {
for (int p = 2; p < MAX_NUMBER; p++) {
if (prime[p] == 0)
prime[p] = 1;
int c = 2;
int mul = p * c;
for (; mul < MAX_NUMBER;) {
prime[mul] = -1;
c++;
mul = p * c;
}
}
}
void print_all_prime() {
int c = 0;
for (int i = 0; i < MAX_NUMBER; i++) {
if (prime[i] == 1) {
c++;
if (c < 4) {
switch (c) {
case 1:
cout << c << "st prime is: " << i << endl;
break;
case 2:
cout << c << "nd prime is: " << i << endl;
break;
case 3:
cout << c << "rd prime is: " << i << endl;
break;
default:
break;
}
}else
cout << c << "th prime is: " << i << endl;
}
}
}
int main() {
gen_sieve_prime();
print_all_prime();
return 0;
}输出
1st prime is: 2 2nd prime is: 3 3rd prime is: 5 4th prime is: 7 5th prime is: 11 6th prime is: 13 7th prime is: 17 8th prime is: 19 9th prime is: 23 10th prime is: 29 11th prime is: 31 12th prime is: 37
更新于：30-Jul-2019
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