c - Pass by reference and pointers

What is the difference between passing by reference the parameters in a function and passing pointer variables as a parameter in a function ?

Answer

There is no pass by reference in C, it's always pass by value.

C developers can emulate pass by reference, by passing the pointers to a variable and the accessing it using dereferencing within the function. Something like the following, which sets a variable to 42:

static void changeTo42 (int *pXyzzy) {
    *pXyzzy = 42;
}
:
int x = 0;
changeTo42 (&x);

Contrast that with the C++ true pass by reference, where you don't have to muck about with pointers (and especially pointers to pointers, where even seasoned coders may still occasionally curse and gnash their teeth):

static void changeTo42 (int &xyzzy) {
    xyzzy = 42;
}
:
int x = 0;
changeTo42 (x);

I would implore ISO to consider adding true references to the next C standard. Not necessarily the full capability found in C++, just something that would fix all the problems people have when calling functions.