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2.2  Pointers

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The value of a POINTER variable is the ADDRESS of a value of another type.  In this case, the type of value contained at this address must be stated.  The '*' qualifier used here declares the variable f_ptr to be a pointer to a floating-point value:

    float    *f_ptr;

Whenever a pointer variable is used, a non-pointer value must be declared as well, in order to allocate machine addresses to contain the data to be pointed to.  Two operators are commonly used in expressions involving pointers:  '&' ("address of") and '*' ("that which is pointed to by").

    float    amplitude = 100.;
    float    *f_ptr;
    f_ptr = &amplitude;
    amplitude = *f_ptr/2.;

These statements declare a pointer 'f_ptr' to a float, as well as a float 'amplitude' which is initialized here to 100.  (It is legal to include an initialization in such declarations.)