const用法及assert

//const的使用
//作用：定义常变量，不允许修改其值 。例如 int const ca = 10;
//1、基本的数据类型对于const是透明的。
int const ca = 0;const int cb=0;
ca和cb是等价的
//2、const 限定它的直接右边
//3、权限可以缩小或者同等传递，但不能放大

int main()
{
int a = 10;
int b = 20;
const int ca = 10;
const int cb = 20;
int *p1 = &a;
//int *p2 = &ca;//error
const int *p3 = &a;
const int *p4 = &ca;
int *const p5 = &a;
//int *const p6 = &ca;//error
return 0;
}

int main()
{
int a = 10;
a = 20;
int b = 20;
int const ca = 10;
//ca = 20;//error
//ca = 10;//error
//int const cb;//error
const int cb = 10;//完全等同ca
//cb = 20;//error
int * p = &a;
const int *cp = &a;
//*cp = 100;//error//直接右边不能做左值
cp = &b;
int *const cp2 = &a;
//cp2 = &b;//error,直接右边不能做左值
*cp2 = 100;

int const *cp3 = &a;//cp3等价cp
cp3 = &b;
//*cp3 = 100;//error
const int *const cp4 = &a;
//cp4 = &b;
//*cp4 = 100;

return 0;

}

assert(表达式)：断言，如表达式为真则什么都不做
#include<assert.h>
eg:assert(b!=0) 断言b一定不等于0