In lab we learned that functions can return values.  For example: 

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#include <iostream>
using namespace std;

int cubed(int x){
    return x*x*x;
}

int main(){
    int y;
    cin >> y;
    cout << cubed(y);
    return 0;
}
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With an input of 2, you should get the answer 8 on the screen.

We also learned the difference between pass-by-value and
pass-by-reference.  For example:

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#include <iostream>
using namespace std;

int cubed(int x){   //pass by value
    x = x*x*x;
    return x;
}

int cubed2(int &x){ //pass by reference
    x = x*x*x;
    return x;
}

int main(){
    int y;
    cin >> y;
    cout << cubed(y) << endl;
    cout << y << endl;
    cout << cubed2(y) << endl;
    cout << y << endl;

    return 0;
}
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With an input of 2, you should get the following:

8
2
8
8

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With the above, do the following problems:

1) Write a program to calculate n! with a function that 
    returns the final answer.
2)  Write a function that takes in 2 numbers from the 
    user and reflects the answer in main (pass by reference).
3)  Write a function that calculates the hypotenuse of a 
    right triangle and returns the answer.
4)  Write a function that swaps two numbers and reflects 
    the change back in main.

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You only need one program [main] to test each of the 
functions.  You can also use (2) to get the numbers 
for (3) and (4).

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Due: TBA