/*

 why use const

 a)Guards against inadvertent write to the variable

 b)Self documenting

 c)Enables compiler to do more optimization,making code tighter,faster

 d)const means the variable can be put in ROM

 */

 //const

 // A compile time constraint that an object can not  be modified

 int main()

 {

     const int i = ;

     //i = 7; wrong

     //如何修改i的值呢？

     const_cast<int&>(i) = ;

     int j;

     static_cast<const int&>(j) = ;//wrong，此时j被转成const

     const int *p1 = &i;//data is const,pointer is not

     p1++;

     int * const p2;//pointer is const,data is not

     const int* const p3;//data and pointer are both const

     int const *p4 = &i;

     const int *p4 = &i;

     //If const is on the left of *,data is const

     //If const is on the right of *,pointer is const

 }