小括号里从左往右

int x, y, z;
int a = (x = 10, y = 40, z = x + y);
cout << z << ' ' << a; //50 50

宏展开

#include <iostream>
#define MA(x) x*(x-1)

using namespace std;
void main()
{
    int a = 1, b = 2;
    cout << MA(1 + a + b) << endl; //8
}

变成了 1+a+b*(1+a+b)

工程里有

do{...}while(0)

C语言数组退化成指针

// 退化 成了地址 所以传进来的参数加一个长度
void f1(int arr[10])
{
    cout << sizeof(arr) / sizeof(arr[0]) << endl; //1
}

int main()
{
    int array1[] = { 1,2,3,4,5,6,7,8,9,10 };
    cout << sizeof(array1) / sizeof(array1[0]) << endl; //10
    f1(array1);
}

C++ 使用容器及引用

C语言移位

char a1 = 0x63;         // 0110 0011
printf("0x%x\n", a1);
a1 >>= 4;
printf("0x%x\n", a1); // 0000 0110 逻辑右移

a1 = 0x98;              // 1001 1000
a1 >>= 4;
printf("0x%x\n", a1); // 0xfffffff9 算术右移

unsigned char a2 = 0x98;// 换成unsigned 
a2 >>= 4;
printf("0x%x\n", a2); // 0x9

所以只有unsigned才能右移，同时注意别移过头了

C++使用bitset

bitset<8>a3 = 0x98;
a3 >>= 4;
cout << a3 << endl;

C的强制类型转换

比较大小不要有无符号类型

unsigned int a1 = 1;
if (a1 > -1)
    cout << "yes" << endl;
else
    cout << "no" << endl;