I have had the recent pleasure to explain pointers to a C programming beginner and stumbled upon the following difficulty. It might not seem like an issue at all if you already know how to use pointers, but try to look at the following example with a clear mind:
int foo = 1;
int *bar = &foo;
printf("%p\n", (void *)&foo);
The unary operator * is the indirection or dereferencing operator; when applied to a pointer, it accesses the object the pointer points to. […]
The declaration of the pointer ip,is intended as a mnemonic; it says that the expression
int *ipis an int. The syntax of the declaration for a variable mimics the syntax of expressions in which the variable might appear.
int *ip = 1
For your student to understand the meaning of the
* symbol in different contexts, they must first understand that the contexts are indeed different. Once they understand that the contexts are different (i.e. the difference between the left hand side of an assignment and a general expression) it isn't too much of a cognitive leap to understand what the differences are.
Firstly explain that the declaration of a variable cannot contain operators (demonstrate this by showing that putting a
+ symbol in a variable declaration simply causes an error). Then go on to show that an expression (i.e. on the right hand side of an assignment) can contain operators. Make sure the student understands that an expression and a variable declaration are two completely different contexts.
When they understand that the contexts are different, you can go on to explain that when the
* symbol is in a variable declaration in front of the variable identifier, it means 'declare this variable as a pointer'. Then you can explain that when used in an expression (as a unary operator) the
* symbol is the 'dereference operator' and it means 'the value at the address of' rather than its earlier meaning.
To truly convince your student, explain that the creators of C could have used any symbol to mean the dereference operator (i.e. they could have used
@ instead) but for whatever reason they made the design decision to use
All in all, there's no way around explaining that the contexts are different. If the student doesn't understand the contexts are different, they can't understand why the
* symbol can mean different things.