Re-open a space for the received variable x

Assign the value x of the variable to this space

All operations on this variable within the sub-function are operations on numbers in the newly opened space.

After the sub-function is finished running, the newly opened space is released.

The address of the newly opened space node x is different from the address of the actual parameter x

In the main function, the value of the x address has not changed. The operation of x in the main function by the sub-function is invalid.

If you insist on calling, it is the same as not calling

The actual parameter passed is the address

The formal parameter defines a pointer

The address of the actual parameter is stored in the space opened by the formal parameter.

The use of formal parameters by sub-functions is to indirectly change the value of the actual parameter based on the address in the formal parameter.

Example: typedef struct student {}node, *list

Within the main function: list l; creat( l);

Subfunction: void creat( list &l ){}

Although there is & in the sub-function, it can be ignored within the sub-function.

Example: pop(stack *l, int *x)

push to stack

pop