Computera machine that under the control of a
program does
a. input,
b. processing (like arithmetic operations or
comparisons or spell checking),
c. output( like the list of misspelled words),
d. saving of the results for later use.
Program- a structured combination of data and instructions
that is used to operate a computer
Hardware: the computer’s physical components
For input- keyboard, mouse
For processing- CPU, motherboard, random access
memory
For output-monitor, speakers, printers
For storage -floppy disks, CDRW’s, hard drive
Software- computer programs, a list of instructions that tell
the computer what to do.
Divided into system software( like operating systems and
utilities)and applications software(word processing)
Programs implement “algorithms”- step by step procedures
to perform a specific task, essentially a recipe
a.
an algorithm for making a peanut butter
sandwich
b.
an algorithm of how to determine the average
of a bunch of test scores
c.
an algorithm to determine which card is
missing from a deck of 51 cards
d.
an algorithm how to drive from Willowbrook
Mall to WPU.
Can your car understand these directions? Does it
think?
You translate these directions into a sequence of
a.
turning the key
b.
pressing on the gas pedal
c.
pressing on the brake pedal
d.
turning the steering wheel
These are translated by the inner workings on the
car to
Applying brake pads,
turning axles,
causing pistons to turn,
causing sparkplugs to operate
Similarly, we can described algorithms like “averaging” 10
grades using short, English like statements, called pseudo
code.
a.
b.
c.
d.
Read in 10 grades
Compute the sum of the 10 grades
The average is the sum divided by 10
Print out the average.
Some people prefer to describe their algorithms using
flowcharts, a description that uses specifically defined
graphical symbols as in:
start
Set sum to zero
Read grade
Add grade to
sum
10 grades
read yet
Average is sum/10;
print it
end
Flowchart for eating pizza.
start
Eat slice
Any
slices
left?
Put pizza box in
garbage
end
Still
hungry
Put leftover slices in
refrigerator
But just as a car might not respond to “go right”, a
computer must be addressed in a way it can handle.
A programming language is a set of instructions, data, and
rules that can be used to construct a program.
The averaging pseudo code or flow chart might be written
in the C++ programming language as
sum=0.0;
counter=1;
while(counter<=10)
{
cin >>grade;
sum =sum+grade;
//add grade to sum
counter=counter+1;
//add 1 to counter
}
average = sum/10;
cout << “the average is “ << average;
But like the car, where a turn of the steering wheel really
turns the tires, the computer needs this higher level
language to be translated into “machine code”, a sequence
of 1’s and 0’s, indicating current flowing and not flowing
in various locations of the computer.
The translating program is called the “compiler”.
Compilers translate a sequence of instructions written in a
higher level language or source code, like C++, into
machine language or object code.
Pseudo code -> higher level language -> machine
language
The C++ statement:
If (income <10000) tax= .03*income
Might be compiled into several machine language
statements that look like
0110000100011010
0100000100001110
1101010101010100
1011101101010001
Higher level language like
C++
English like commands,
arabic numbers
Machine independent
One statement
Less efficient because
cannot take advantage of
architecture
Symbolic locations
Machine language
Composed of 0’s and 1’s
Specific to machine
Different for IBM, Apple
Many statements
More efficient
Specific numbered locations
Compilers translate a whole higher level language program
(many statements)to object code, that is then “executed”
An interpreter translates one source statement at a time
into executable statements. Each statement is executed
immediately after translation.
good for finding errors,
object code tends to be less efficient.
Ex. Basic
As English has syntax (grammar and spelling)rules and
semantic(meaning) rules, so do programming languages.
In English it is grammatically incorrect to write
The student eat a apple?
and it does not make much sense to write
The house eats the moon.
Each programming language has its own set of rules.
The statement in C++
sum= sum+grade;
is grammatically correct, but the following are incorrect:
sum+grade =sum;
sum= sum+ grade
(missing the semicolon)
In PASCAL we would write
sum:= sum +grade;
All programming languages have ways of
Reading data
Writing results
Assigning expressions to variables
Asking questions and selecting results
Looping when the terminating condition is known
beforehand
Looping when the terminating condition is not known
beforehand
Doing arithmetic
Dividing a big problem into smaller subproblems
using a procedure, a logically consistent set of instructions
that produces a specific result.
But they might have slightly different ways of expressing
these concepts.
Until the last decade , most languages were procedure
orientedinterested in implementing algorithms.
Emphasis was on how something was done
how well it was done.
Possibly because of a large amount of graphics
programming, languages have become object oriented
If you do graphical text processing as I did when
making the flow charts, one is given
a set of objects- like diamonds, rectangles, ovals,
arrows
a set of operations-putting in text, increasing their
size, rotating the object, moving the object.
In object-oriented programs, these general shapes and
procedural characteristics are examples of classes, and
each instance is an object. The procedures contained within
an object are called member functions or methods.
C++ is an object oriented language that grew out of C,
a procedure oriented language.
In CS 230 we will essentially confine ourselves to the
parts of C++ that are found in C.
In CS240, the object oriented part will be introduced.