CIS 130 - Week 8, Wednesday, 03-10-10

*   I'd like to write a function for the area of a ring...

*   (note: I HAVE the circ_area function available...!)

*   OK, I know that if I'm given the ring's "outer" radius,
    and the radius of its "hole", then I have everything I need
    to compute its area...

*   // contract: ring_area: double double -> double

*   // purpose: expects the outer radius of a ring and
    //          the radius of its "hole", and produces
    //          the area of that ring

*   its header:
double ring_area(double outer, double inner)

*   examples:
ring_area(10, 1) == circ_area(10) - circ_area(1)
ring_area(10, 1) == 311.01741

*   named constants:
    ...turns out, since I'm using circ_area thst already defines PI,
       I *don't* need to redefine it here;
       (in fact, I SHOULDN'T redefine it, because C++, like Scheme
       does NOT like it if you define the same name twice in the
       same scope)

*   body:

{
    return circ_area(outer) - circ_area(inner);
}

*   Not all C++ functions involve numbers...
    let's write one that just involves strings.

    note: + used between two string expressions will
          produce concatenation of those 2 strings
	  (or, one string consisting of both)

    "alp" + "ha" --> "alpha"

*   Let's say I'd like a function that expects two
    strings, a first name and a last name, and produces
    a single string that is a "pretty" form of that
    full name:  last_name, first_name

*   contract: pretty_name: string string -> string

*   purpose: expects a first name and a last name,
             and it produces a single string
	     that is <last_name>, <first_name>
	     (the last name, then a comma and a blank,
	     and then the first name)

*   header:
string pretty_name(string first, string last)

*   examples:
pretty_name("Frank", "Rizzo") == "Rizzo, Frank"

*   body:
{
    return last + ", " + first;
}

*   how about conditionals?

*   the most basic C++ conditional statement is the if statement

*   in Scheme:
    
    (cond
        [test1 result1]
        [test2 result2]
	...
	[else result-else]
    )

    You could do the same thing as the cond above in C++ with the
    following:

    if (test1)
        return result1;
    else if (test2)
        return result2;
    ...
    else
        return result_else;

    or -- if you might ever do more than 1 thing because of a test...

    if (test1)
    {
        return result1;
    }
    else if (test2)
    {
        return result2;
    }
    ...
    else
    {
        return result_else;
    }

*   CLASS CODING STYLE STANDARD:
    each curly brace is on its OWN line,
    lined up (the opening brace lined up with the preceding line),
    with the statement(s) within indented by 3 or more spaces.

    *   you only NEEEED the { } when the action takes more than 1 statement

*   the simplest if statement in C++:

    if (test)
       action;

    *   ...more COURSE STYLE: the action for an if is on its OWN line,
           even if we don't use the curly braces...

    *   semantics:
        if test is true, do action;
        otherwise, just skip the action and go on.
    
    *   the else is optional:

    if (test)
       if_action;
    else
       else_action;
    
*   COURSE STYLE: the else's action should be indented
    also! (even if no curly braces)

    if (test)
    {
        action1;
	action2;
    }

    if (test)
    {
        action1;
	action2;
    }
    else
    {
	action3;
	action4;
	action5;
    }

    ...I'll do action1 and action2,
       OR action3, action4, action5 --- NEVER all 5!!!

*   MORE STYLE: WHEN it is a choice of 3 or more options,
    use the style we first demonstration:

    if (test1)
        action;
    else if (test2)
        action2;
    else if (test3)
        action3;
    ...
    else
        action_else;