CSCI 15A                                               Jim Murphy

The C++ compiler breaks your source code into tokens
according to the rules of syntax of the language


These smallest program units include:

Special symbols of one or two characters
such as //  +  {  +=  <= etc.

(Tokens are separated by space or carriage returns or
special symbols or comments)

Keywords such as int, return, struct, if, while etc.
see page 583 for a complete list.

int try = 1;

Identifiers such as main, customer, cin etc.
names of classes, objects, and functions
Start with a letter then any number of letters,
numbers and underbars _
Number of characters distinguished by the compiler
depends on the compiler (some use 32 characters)
float CostOfThisItemToYouWhenYouComeByOnMonday;
float CostOfThisItemToYouWhenYouComeByOnTuesday;
float s, x, t, b1, CostOfItem, Cost_of_Item;
/*
Constants such as -7, 23, 2.56, 'C', "Hello" etc.
“A+”  “int”  “float”
Comments either all after // on a given line or
everything between /* and */ possibly several lines
*/
Objects supported include float, int, and char
each object must be declared (optionally initialized)

class-name  object-identifier-list;
int x, y, z;
float cost, tax, interest;
char grade;

class-name  object-identifier = expression;
int sum = 0, x, y, z=0;
char MidInitial = 'L';
float rate = 0.0825;

Assignment to already declared objects with
object-identifier = expression;
// in compiler terms   lvalue = rvalue;
evaluate the expression on the right and assign
the result into the memory location of the object
named on the left

can be used to alter the state of objects:
sum = sum + cost;
float tax = 5; //  int 5 is converted to float 5.0
int  count = 2.73; // count becomes 2

const object-initialization  // will keep you from
accidently changing a value later in the program

const float pi = 3.1415926;
If you omit the class then int is assumed and for

const interest = 0.0875;

interest will be taken to be an integer and the
type conversion will make interest zero

Arithmetic expressions include:

numeric constants: 7, -2, 3.78, 2.74e-3
- expression
expression op expression where op is +,-,*,/,%
(expression) such as -(3 + 5)

LESSON 3

higher precedence for:
*  /  %   evaluate left to right
then
-  +     evaluate left to right

6 - 2 + 4 / 2  is  4 + 2  not  8 / 2

7 / 2 = 3 is an integer division
7 % 2 = 1 is the remainder after integer division

mixing int and float the int is promoted to float
7 / 2.0 = 3.5
any of these examples could have been given 
using object names such as:
int x = 7;  x / 2 would then be 3
Read all the exercises - try the ones that are not
obvious - in class look at 4 and 5 pages 47 and 48

(15)Second assignment due June 5, 1996.
Start from your personalized template file and write
a C++ program on unix to solve lab project 2E on
page 52.  Then use ftp on the PC to transfer the
source code to the 486 machine in OCNL 133 and
compile there or to a PC or MAC at home.
In Windows put the source file in a directory of by
itself and within BC++ create a new project with
the same name - use EasyWin as the target.
Hand in a listing of your program, a print of the
window containing your run on unix and Windows.

In Windows put the source file in a directory by
itself and within BC++ create a new project with
the same name - use EasyWin as the target.
email a listing of your program, a paste of the
window containing your run on unix and Windows.

Programming Errors can be:
Compiletime, Linktime, Runtime, or of Intent

Compiletime errors are detected by the compiler
when it has trouble with your syntax (language rules)

int student Number;
cin >> student;
missing comma between student and Number
the real error may be that studentNumber is intended
to be all one word - then we drop space and also
cin >> studentNumber;
Notice if we had:

int student Number;
cin >> studentNumber;

both lines would generate errors since the space in
the first line causes studentNumber to be an
undeclared object.

Some errors appearing later in the code will make
no sense and will disappear when the earlier errors
are fixed - also note that you will likely get quite
different errors from different compilers

Linktime errors are found by the linker when it
attempts to put several modules together and can
not find certain functions or objects that are referred to
such as "Undefined symbol _main"
if you are missing:
int  main ( )
in your program - perhaps because you have:
int Main ( )  or some other unacceptable variation

Runtime errors can occur if you have something like:
int denom;
cin >> denom;
cout << 8 / denom;
if denom should be entered as zero this will cause
a runtime error
Later we will see how to check for this and avoid it

Errors of intent occur because computers do what
we tell them to do not what we want them to do

These errors are the most difficult to discover but
testing known cases can help

Try introducing known errors into the programs you
have worked with so far and try compiling the 
faulted programs with various compilers to see
what errors you get if any.  Notice many changes
to programs will not cause errors to be generated.

In other words there are many statements which while
legal in the language are not what you want. 
Typically only one statement is really correct.
This is not to be confused with the fact that there
are many approaches to solving any problem but that
in the context in which the statement is found most
of this flexibility is lost

Find the classnotes in the directory:

/usr/local/gx/mercer/classnotes
or on the web site