C语言如何判断一个数是否为素数

#include <stdio.h>

#include <stdbool.h>

int main(void)

{

unsigned long num; //要检查的数

unsigned long div; //可能的约数

bool isPrime;

printf("Please enter an integer for analysis: ");

printf("Enter q to quit.\n");

while(scanf("%lu", &num) == 1)

{

for(div=2, isPrime = true; (div * div) <= num; div++)

{

if (num % div == 0)

{

if ((div * div) != num)

printf("%lu is divisible by %lu and %lu.\n", num, div, num/div);

else

printf("%lu is divisible by %lu.\n", num, div);

isPrime = false; //不是一个素数

}

}

if (isPrime)

printf("%lu is prime\n", num);

printf("\nPlease enter another integer for analysis: ");

printf("Enter q to quit.\n");

}

printf("\nBye.\n");

return 0;

}

以上来自书籍《C Primer Plus》中文版第五版 163页