Ways to pass variables to functions in C

There seems to be a confusion among people (even authors of Many books) about ways of passing values to a function.
Question: How many ways are there to pass a variable to a function in C ?
Ans: proposed by most people (authors) :

• Passing variables by values
• Passing variables by references

My Reaction : Wrong !!!!!!!
To make thing even worse, the example most writer put up for passing values by references is this :
 

#include<stdio.>

void swap(int *x, int *y)
{
     int* t;
     *t=*x;
     *x=*y;
     *y=*t;
}

int main()
{
    int x,y;
    x=100;
    y=200;
    swap(&x,&y);
    printf("%d,%d",x,y);
}

I don't know if you get this example or not, But this example is wrong.

This example is using pointers, and pointers are not references.
So again:
Question: How many ways are actually there to pass variables to functions in C ?
Well there is only one way: Passing variables by value.

Question: But What about books claiming that variables can be passed to functions by references?
Ans: Well I don't know what other authors are writing or why they are writing such information and feeding it to students. I think many writer confuse pointers and references to be same, they are not.
There is a good article on Wikipedia about this :  c++ references
To simplify pointers and references : Always remember
Pointers can be created without initializing them (meaning they can have garbage) while references can't. References are to be initialized as soon as you create them. But funny thing is C doesn't have references !!. This can be easily proven by using gcc compiler, declare a reference variable and watch gcc complaint during compilation(easy).
Question: So what about the example above?
Well technically the example is not using references (cause C don't have them). But passing values by reference is a good feature to have (unfortunately C doesn't have this feature). So how will you simulate this behavior in C? Well by using pointers.
By explicitly passing the address of variable, our function can do anything with that variable. But it should be noted that these addresses are again passed by value ( since addresses are nothing but integers and C can only pass variables by value only). This is the reason why we can't modify the address we have passed in C to a function (cause it was passed by value).
Comment if you didn't or did get what I was trying to convey.