打印素数 两种不同方法

1.用数组列出素数表 是素数该下标对应的值为1 将每个素数的倍数对应的下标值赋为0 这样就完成了素数表

#include <stdio.h>

int main(){
    const int maxNumber = 255;
    int isPrime[maxNumber];
    int i;
    int x;
    for (int i = 0; i < maxNumber; ++i) {
        isPrime[i] = 1;
    }
    for (x = 2; x < maxNumber; ++x) {
        if(isPrime[x]){
            for ( i = 2; i*x<maxNumber; ++i) {
                isPrime[i*x] = 0;
            }
        }
    }
    for (i = 2; i < maxNumber; ++i) {
        if(isPrime[i]){
            printf("%d\t",i);
        }
    }
    printf("\n");
    return 0;
}

2.用素数能否被之前的素数整除用来判断

#include <stdio.h>

int isPrime(int x,int knownPrimes[],int numberOfKnownPrimes){
    int ret = 1;
    int i;
    for (i = 0; i < numberOfKnownPrimes; ++i) {
        if(x % knownPrimes[i] == 0){
            ret = 0;
            break;
        }
    }
    return ret;
}

int main(){
    const int number = 100;
    int prime[number] = {2};
    int count = 1;
    int i = 3;
    while (count < number) {
        if(isPrime(i, prime, count)){
            prime[count++] = i;
        }
        i++;
    }
    for (i = 0; i < number; ++i) {
        printf("%d ", prime[i]);
    }
    printf("\n");
    return 0;
}