double x = 3.14159;
printf("%.3f\n", x);Correct format specifier for double in printf
printf("%.2f\n", -0.0000000001);会输出-0.00。
有时这样的结果是错误的。在没有Special Judge的题目要求四舍五入时，不要忘记对负零进行特殊判断。
#define LOG2(x) (31 - __builtin_clz(x))#define PARITY(x) __builtin_parity(x)#define POPCOUNT(x) __builtin_popcount(x)//returns the number of non-zero bits in x
F(n) = (n - 1) * (F(n - 1) + F(n - 2)) F(n) = n * F(n - 1) + (-1) ^ n
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