素数
#include <math.h>
#include <stdio.h>
int main(void)
{
int number, flag=1, i;
printf("Input n:\n");
/*************** Begin ***************/
scanf("%d", &i);

/*************** End ***************/
if (flag != 0)
{
printf("%d is a prime number\n",number);
}
else
{
printf("%d is not a prime number\n",number);
}
return 0;
}
# include <stdio.h>

int main(void)
{
int i, j;

printf("Input n:\n");
scanf("%d", &i);

for (j = 2; j <= i; j++) //保证除数是在2~被除数中间的一个数
{
if (i % j == 0) //被除数刚好能被整除
break;
}
if (i == j) //确定能将被除数整数的是否是被除数本身，若是本身则是素数，若不是则是合数
printf("%d is a prime number\n", i);
else
printf("%d is not a prime number\n", i);

return 0;
}