### 快读快写
 ```c++
 x << 1 == x * 2; 
 x << 3 == x * 2 * 2 * 2;
 ```
二者相加也就是 `x * 10`;
 
 (1) 设$ch='3'$   $ASCII= 51 =  00110011(b)$
 (2) 字符 $'0'$ 　$ASCII= 48 =  00110000(b)$
 
 `^`运算规则：同$0$ 异$1$，相同的两个数异或为$0$ 不同的异或为$1$
 
 `ch^48` 相当于 `ch -= '0'` ，得到 $00000011$,即数字$3$


```c++
//快读
inline int read() {
    int x = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-') f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        x = (x << 3) + (x << 1) + (ch ^ 48);
        ch = getchar();
    }
    return x * f;
}

//快写
inline void write(int x) {
    if (x < 0) putchar('-'), x = -x;
    if (x > 9) write(x / 10);
    putchar(x % 10 + '0');
}
```