MESSAGE
| DATE | 2010-02-19 |
| FROM | Ruben Safir
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| SUBJECT | Subject: [NYLXS - HANGOUT] C++ Workshop _ Syntax Basics
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C++ Integer types - Data Representation
Constant and Literal Integers are represented as numbers without any
quotes. They can be represented in decimal, octal, and Hexadecimal
forms. They can be assigned to int, short, long and signed and unsigned
variables and they are literal, and therefor can not be left values: ie
values that go on the left of an assignment operator.
Decimal Forms look like these examples:
int i = 255;
short i = 255;
long i = 4000;
unsigned short = 32;
signed int = -273;
Octal examples are similar to the integers that we saw with chars and
begin with zeros:
int o = 042;
short o = 0101;
long o = 0076;
unsigned o = 0101;
singed long o =011102;
Hexadecimal examples begin with x or X and again are without quotes:
int h = 0xFF;
short = 0x12;
long = 0xA2E44D;
unsigned = 0xA2;
signed long = 0xAF23E4;
Integers also have the ability to be expressed as Unsigned or Long
literal values, if the need arises to do so.
unsigned regist = 121U;
long lightspeed = 123456789L;
#define MAXVAL 1234567U
While discussing integer values, the programmer also needs to be aware
of the size_t typedef that C and C++ uses for the sizeof() operator.
The sizeof() operator returns the size of any data object in size of
bytes. Its return value is an integer of type size_t. Because in C
and C++ we manage memory directly, the sizeof() operator plays a
significant
role in your programming. And example of sizeof() is:
size_t i = sizeof(oint);
One of the unusual properties of integers and chars is that both
represent
real integer values. As a result, many of the mathmatical operators can
be
used with them and they can be assigned to each other. There are
automated
rules for "recasting" the data types as they interact with each other.
We'll
look at this rules in detail later. But for now one should be aware
that statements theses are common in C and C++.
char letter, letter2;
int number;
short num2;
long num3;
letter = 'c';
letter2 = 'G';
letter++; //now stores 'd'
cout << letter << " " << endl; //prints 'd' and a line feed
num2 = letter;
cout << num2 << " " << endl; //prints '100' and a line feed
cout << letter + leter2;
Floating Point
Floating Point data essentially can be represented in the two styles
already discussed, as decimal and scientific notation. Decimal notation
can be followed by an 'F' or 'f' for single precision or a double
precision with an 'L' or 'l' (not a 'D' for double). Here are some
examples:
double avog = 6.23xE23;
float pizza = 0.125;
float trip = 102.7F
float population = 8,323,456L;
float pop_brklyn = 8.32xE6;
Casting:
C and C++ are typed languages, but they have some flexibility built into
their design in this regard. This can be good and bad, because this
also means that the language will give you room to hang yourself if you
don't learn the explicit rules for the accommodations that C++ will make
for you. For example, one can assign a float into an integer - but then
you are left to understand what the resulting outcome is. And these
are very difficult bugs to catch because the code looks correct, seems
logical, and it is a raw syntax error.
For example, what does this legal code do?
#include
#include ;
int a,b,c,z;
float d,e,f;
a = 1.25;
b = 2.50;
c = 5;
d = 0.6125;
e = 0.30625;
f = 0.153125;
z = 25U + 75;
z = z * a;
cout << b/2 << endl;
z=((pow(b,2)) + e)/((pow(f,e)) * z);
cout << "I have no clue what this results in and can't be paid enough to
debug it " << z << endl;
Rules for Casting:
Implicit Rules:
When the compiler is confronted with two different data types, it tries
to work operations by casting one data type to another which is
compatable to the expression. The programmer can also manually do such
casting. The Implicit casting rules are as follows:
There are 4 events that trigger C and C++ to do implicit type
conversion:
A) When the operants in a mathmatic or logic expression are of two
different type: example
char a = 'A';
int b = 9;
long c;
c = a + b;
if(c == b){
//do something
}
B) When the assignment on the right side of an equation doesn't match
the type of the variable or lvaue on the left: example
char a = 'a';
double b;
b = c;
C) When the argument to a function or method doesn't match the
parameter.
We will see this when we look at functions.
D) When the return statement doesn't match the function type. Again, we
will see this when we examine functions.
Rules:
Generally the implicit cast rules are designed to loose the least about
of
precision possible. If an arithmatic operation includes floating
point data then the implicit casting of data follows the following rules
float --promotion-->double-->long double
Neither operand in an arithmatic operation has a float:
int-->unsigned int-->long-->unsigned long : Note that these promotions
can lose there sign (lose negitivity). I also note that when attempting
to verify these promotion rules in C and in C++, that they don't hold.
I can not create an example program that will promote the signed data
type to an unsigned one, and to then lose the sign.
--
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