Variable types with * prefix

[sterretje]

@GolamMostafa

int y; //it is a declaration; no memory space is allocated

It's a definition; memory is allocated. Below is a variable declaration

extern int y;

No memory is allocated; it's your responsibility to allocate it (read: create a variable of the same type with the same name) elsewhere.

See e.g. Difference between Definition and Declaration - GeeksforGeeks