Page 67 - DCAP201_FUNDAMENTALS_OF_DATA_STRUCTURES

Fundamentals of Data Structures

Notes
Figure 5.1: Pointer, Variables and Memory

Source: http://www.cs.cf.ac.uk/Dave/C/node10.html
Now the assignments x = 1 and y = 2 obviously load these values into the variables. ip is declared
to be a pointer to an integer and is assigned to the address of x (&x). So ip gets loaded with the
value 100.
Next y gets assigned to the contents of ip. In this example ip currently points to memory location
100 — the location of x. So y gets assigned to the values of x — which is 1. We have already seen
that C is not too fussy about assigning values of different type. Thus it is perfectly legal (although
not all that common) to assign the current value of ip to x. The value of ip at this instant is 100.
Finally we can assign a value to the contents of a pointer (*ip).
When a pointer is declared it does not point anywhere. You must set it to point somewhere
before you use it.
So ...
int *ip;
*ip = 100;
will generate an error (program crash!!).
The correct use is:
int *ip;
int x;
ip = &x;
*ip = 100;
We can do integer arithmetic on a pointer:
float *flp, *flq;
*flp = *flp + 10;
++*flp;
(*flp)++;
flq = flp;

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