C :: Finding Largest / Smallest / Average In A Loop

I'm trying to write a program that will allow a user to enter infinite numbers (one at a time) with a way to stop entering values, and once it stops it immediately displays:

Lowest number:
Highest number:
Number of values entered:
Average of numbers:

what I can't figure out is:

-how to end the loop with something other than a number, preferably a char, so that it doesn't affect the average/lowest/highest

-how to output the lowest and highest numbers in a loop (would be easier to figure out were it finite and I could just type a bunch of printf/scanf)

What I have so far:

Code:

#include <stdio.h>#include <stdlib.h>
#define pause system("pause")
main(){
//n = amount of numbers input
//x = number given by user
//s = smallest number
//l = largest number
}

[code].....