When it modifies a data declaration, the const keyword specifies that the object or variable isn't modifiable.
https://learn.microsoft.com/en-us/cpp/cpp/const-cpp?view=msvc-170
https://learn.microsoft.com/zh-tw/cpp/cpp/const-cpp?view=msvc-170
basic
//const declar
int i = 42;
const int j = i;
int k = j;