输入一个大于1的数，判定它是不是素数

#include <stdio.h>
#include <math.h>

int main()
{
int b,c1 = 1,again = 0;
while(again == 0)
{
printf("请输入数字\n");
scanf("%d",&b);
double c2 = sqrt(b); //对b进行初始化，并给c2赋值

    while(b<1) 
    {
        printf("格式不符，请重新输入\n");
        scanf("%d",&b);
    }
    
    while(b>c1 && c1<c2) 
    {
        if(b%c1!=0)
        c1++;
        else 
        {
            printf("%d不是素数\n",b);
            break;
        }
    }
    if(c1>=c2)
    printf("%d是素数\n",b);
    again++;
    printf("***运算结束，重新输入请按0***\n");        
    scanf("%d",&again);    
}
return 0;

}

public static boolean isPrime(int n) {
    if (n <= 3) {
        return n > 1;
    }
    int sqrt = (int)Math.sqrt(n);
    for (int i = 2; i <= sqrt; i++) {
        if(n % i == 0) {
            return false;
        }
    }
    return true;
}