第三题：判断一个数是否是素数,

void main(){ int n; scanf("%d",&n); if (n < 2) { return 1; } int i, m = (int)sqrt(n) + 1; for (i = 2; i < m; ++i) { if (n % i == 0) { break; } } if (i == n) { printf("%d is a primer\n",n); } else { printf("%d is not a primer\n",n); } return 0;}