How do I print the sum of the 5 numbers? And the average?

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your cpde is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.
Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]
1.11 — Debugging your program (stepping and breakpoints) | Learn C++[^]
The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Learn to use the debugger as Patrice wrote and you find your mistakes and missing code.

Tips:
1. count the numbers of input in the loop
2. you must sum up in the loop (because the value got overriden with the next input)
3. output of numbers of input after the loop

Your code should look like this

int main()
{
    int input = 5;
    int sum = 0;
    int count = 0;

    while(input != 0)
    {
        printf("Enter 5 number (0 to stop): ");
        scanf("%i", &input);
        sum += input;
        if (input != 0) ++count;
    }

    //int sum = input;
    float avg = (float) sum;

    if (count != 0) avg /= count;

    printf("Count is: %d\n", count);
    printf("The sum is: %d\n", sum);
    printf("Average is: %.2f\n", avg);

    return 0;
}