.Open Chapter 2: pages 26-42 Variables and Arithmetic 
. Podcast 3
.See ./03.mp3
. Straight Forward Programs
I define a 
.Key straight forward program
as one with the following algorithm:
.List
 Get some input from the user (common but optional)
 Do some calculations
 Send some output to the user
.Close.List

For example:
.Table Input	Output
.Row A positive real number	Its square root
.Close.Table
.See ./02ex0.cpp

The program structure for a straight forward program is, therefore
.As_is 		/* Name and Project
.As_is 		   Algorithm
.As_is 		   Status
.As_is 		*/
.As_is 		#include ...
.As_is 		using namespace std;
.As_is 		declare global constants like PI.
.As_is 		main()
.As_is 		{
.As_is 			Declare variables
.As_is 			Get values for input variables
.As_is 			Do some calculations
.As_is 			Send some output to the user
.As_is		}

. Reading
 *** 2.1 Variables and Reading/writing
 ++ must reserve space for vairables and give them a name -- use a
declaration.
 *** 2.2 Arithmetic
 ++ How to get \pi (PI) into a C++ Program --(PI)
.As_is #include <cmath>
.As_is using namespace std;
.As_is const double PI = 4 * atan(1.0);
 ++++ Programs that use functions in <cmath> will compile but they
will not link unless you compiler command looks like this:
.As_is 		g++ -lm -o pythagoras pythagoras.cpp
(the "-lm" adds the compiled 'm' library to the program).
However, `Q` understands this and does it for you.
 ++++ A common error is to guess that the '^' symbol is for powers.
It isn't!  It is an advanced bitwise logical operator covered in CSCI202.
So to caculate the square of `x` write "x * x", and to cube it "x*x*x".
For higher and unknown powers use the `pow` function from the <cmath>
library:
.As_is 		double nth_power_of_x = pow(x, n);
.Open Syntax
 Elementary steps
.Set
 Reserve storage to hold values in variables -- (declarations)
.As_is 		int v;
(for counting)
.As_is 		double v;
(for measurements)
 Get input from user
.As_is 		cin >> v >> v...;
 Send output to the user
.As_is 		cout << e << e ... ;
.As_is 		cout << "string" << endl ;
 Do a calculation and store the answer.
.As_is 		v = e;
where `v` is any variable name and `e` is any expression.
.Close.Set
 Structures
.Set
 Sequence
.As_is 		{
.As_is 			steps
.As_is 		}
 Selection -- Later
 Iteration -- Later
.Close.Set
.Close
. ++ Tracing a Program
You can not understand a computer program just by reading it.  The only
way to be sure you know what it will do is to pretend to be a computer
and execute the program by hand.   You need a workspace to simulate RAM.
You need a calculator to simulate the CPU/processor.  You then
go thru the program, `step by step`, and use a paper and pencil
to trace each step and what it does to the variables.  Since variables
change values a lot it helps if you reserve a column to record the
values.   It helps if you keep one finger on the code, and record
each step and what RAM looks like.

For example, if you see this bit of code:
.As_is 		int i;
you will need to record a column like this
.Table int i	i
.Row 	?
.Close.Table

After these two steps:
.As_is 		int i;
.As_is 		i = 10;
you will need to record a column like this
.Table int i	i
.Row 	?
.Row i=10	10
.Close.Table
After these three steps:
.As_is 		int i;
.As_is 		i = 10;
.As_is 		i = 2 * i;
you will need to record a column like this
.Table int i	i
.Row 	?
.Row i=10	10
.Row i=2*	20
.Close.Table
.Open Questions
. Were we supposed to read all the sections or just the first two like in
the syllabus

For this class just pages 26-42.

. I don't have any questions today can I ask one one on Thursday
You need to ask a question every class to get credit... even if you think
you know the answer.
. Which is the most important part of the reading.
Please look at the web page for the "***" ratings.  

Note: this question is too general to prove you did the reading.... next
time no credit.

. How can I remember all the special words and rules
Write them down on a single sheet of paper.

You can bring a single such sheet into all quizzes and the final.


. Who figured out how to write expressions
Jim Backus in FORTRAN I...... which lead to the Algols,....B,...C,...C++.

. Who figures out what to write in expressions
Programmers.
. What is the precedence for oprators in C++
It is close to "Please Excuse My Dear Aunt Sally" or
the British "BODMAS" mnemonic.
.List
	Parenthese (and Brackets)
	Multiply and Divide (left to right)
	Add and subtract (left to right)
.Close.List
. Do these precedence change in a program
No.  

. Are there any confusing expressions

Warning: look out for "^" it is not exponentiation.

Warning: Look out for expressions like
.As_is 		2/3
because the computer sees two integers (2) and (3) and so does
integer division giving the answer
.As_is 		0
To get "two-thirds" you need to force the compile to use double
length calclations like this
.As_is 		2.0/3.0
See
.See ./03ex.cpp
for a demo.

. What are real numbers
Talk to the math department!
. Can you have a double constant and how do you do it
Yes.
.As_is 		const double NAME = value;
Example
.As_is 		const double PI = 4*atan(1);

Note -- you can have constants of any type you want.  When ever you learn
about a new type you'll find you can construct constants for that
type of object.

. Does C++ have sigle length vaariables like BASIC
Yes.  They are called 'float' vaariables and declared like this
.As_is 		float x;
.As_is 		float CONST = value;

In this class don't use them -- our computers are fast and big enough
to handle full precision double length calculations.

. What do double and const double do
These reserve space for a double-length number -- ready to do
calculations.  Good for holding measurements.  Vital
when you want to do work with fractions.
They also give the space
a name.
. How do you use double in a program
It's used to declare variables that hold measurements and fractions:
.As_is 		double name;
.As_is 		double name=initial value;

You should always declare a variable before you use it.

. Is writing the declaration first like backwards
Possibly -- but it is needed for the compiler to know what each
symbol means the first time it sees it.

. Is there a limit to the number of variable you can have
No.

. What is the int main()
In some books (and my old examples) the main function is
always written like this:
.As_is 		int main()
rather than Jan's
.As_is 		main()
Both are ok.  The first is very precise.  The second use a
rule that, by default, functions return 'int's.

. Why is the final return not required by the standard
Because if you `had to` have it then thousands of C and old
C++ programs would by non-standard and not compile.  The standards
people (and most compilers) left a loop hole.

. Why aren't complicated math functions included automatically
The take up time to compile and make the compiled program bigger.

When C++ was C it was used mainly for "system programming" and there
was no need for most program to do complex math.

This is even more true about non-elementary functions that can be
found on the Internet... but are not part of the standard.  Most
programs don't need them.

. How is input entered
The program starts to run and stops.  The user types in the input data
and taps the "Enter" or "Return" key.  The program takes what the
user typed and makes it fit (if possible) what is in the `cin` statement.

. Can you solve and math problem in C++
You can solve any `solvable problem` in C++.

One of the big discoveries made in the beginning of computer science
was the discovery that some problems can not be solved by a computer.
These are called 
.Key unsolvable problems
and Turing was able to show that no computer would be able to
solve them.   This is a fascinating and tricky topic
that is covered in the CSci500 level theory classes.

What we can say is that if any machine can do it then C++ can program it.
. Can we make the the input and output look nice like Visual Basic
Yes -- if you get a copy and #include the right library.

Sadly I don't think we'll have time to do this in CSCI201.

On the other hand it is very easy to do once you've got the library.
For example both our KDE linux and MS Windows have nice user interfaces
that let you draw forms and generate code for them. 
. I didnt fully understand ++ and -- on page 39
(1) It is a subtle bit of C++.

(2) The book seems to have a misprint.

C++ lets you put ++ and -- operations inside expressions.  They
always add (subtract) one from a variable, but they also return a
value.  Suppose we have
.Table i	j	k
.Row 2	4	17
.Close.Table
Then after
.As_is 		k = ++ i;
we have
.Table i	j	k
.Row 3	4	3
.Close.Table

If we again start with
.Table i	j	k
.Row 2	4	17
.Close.Table
Then after
.As_is 		k = i ++;
we have
.Table i	j	k
.Row 3	4	2
.Close.Table

Summary of the rules
.Table Expression	Effect on i	Returned value
.Row i+1	None	old i + 1
.Row i++	add 1 to i	old i
.Row ++i	add 1 to i	old i + 1
.Close.Table

. Why is tracing a program helpful
No other method gives you an understanding of what the computer is going to
do.  

It shows that you understand the program and so can earn you points
in a quiz.

. What does cout mean
This variable is pronounced "C out" and it means: the place where
C output is sent.
.Close
. Exercise  -- Tracing a very simple program
What does this program output: 
.See ./02ex1.cpp
. Exercise  -- Tracing a straight forward program
I will show you a straight forward program you predict what it
outputs.
.See ./02ex2.cpp

. Quiz 1
I will give you some straight forward programs
and you work out what they output.

I will also ask you to describe a straight forward program
that you'd like to do as a project: inputs and output. See
.See ./projects.html#P1
. Lab 02 -- Straight forward programs
. Note
The first project is also a straight forward program.  But not one
in the labs or in class!
. Next -- Selections
.Close