starting out with python - chapter 2 ppt
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Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
STARTING OUT WITH
ythonython
First Edition
by
Tony Gaddis
Chapter 2Input, Processing, and Output
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2.1 Designing a Program
Concept:
Programs must be carefullydesigned before they are written.During the design process,programmers use tools such aspseudocode and owcharts to
create models of programs.
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2.1 Designing a Program
The Program Development Cycle•Design the Program
•Write the Code
•Correct Syntax Errors
•Test the Program
•Correct Logic Errors
Figure 2-1 The program development cycle
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2.1 Designing a Program
More About the Design Process
The rocess o! designing a rogram comrises t"oimortant stes#
1.$nderstand the tas% that the rogram is to er!orm
2.Determine the stes that must be ta%en to er!orm
the tas%
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2.1 Designing a Program
More About the Design Process
1.$nderstand the tas% that the rogram is toer!orm
a. &nter'ie" the customer
b. De'e(o the software requirement (a simple task that
the program must perform in order to satisfy the ustomer!
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2.1 Designing a Program
More about the design process
2. Determine the stes that must be ta%en to er!orm
the tas%.
• De'e(o an a(gorithm) a set o! "e((-de!ined (ogica( stes
that must be ta%en in order to er!orm a tas%.
For Exam(e#
Write a rogram to ca(cu(ate and dis(ay the gross ay !or an hour(y
aid em(oyee.
1. Get the number of hours worked.2. Get the hourly pay rate
3. Multiply the number of hours worked by the hourly pay rate.
4. Display the result of the calculation that was performed in step 3.
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2.1 Designing a Program
Pseudocode is an in!orma( (anguage used to de'e(o a
rogram*s design. &t has no syntax ru(es and is not
meant to be comi(ed or executed.
For Exam(e#
Write a rogram to ca(cu(ate and dis(ay the gross ay !or an hour(y aid
em(oyee.
Input the hours worked
Input the hourly pay rate
alculate !ross pay as hours worked multiplied by hourly pay rateDisplay the !ross pay
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2.1 Designing a Program
Figure 2-2 Flowchart for the pay
calculatng program
+ !(o"chart is a too( that grahica((y
deicts the stes that ta%e (ace in
a rogram.
Tyes o! Symbo(s#
•,'a(saear at the to or bottom
o! the !(o"chart) and are ca((ed
termina( symbo(s
•Para((e(ogramsused as inut and
outut symbo(s
•ectang(esused as rocessingsymbo(s
•+rro"sreresent the !(o" o! the
rogram
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2.2 &nut) Processing) and ,utut
Concept:
Input is data that the program
receives. When a programreceives data, it usuallyprocesses it by performing someoperation with it. The result ofthe operation is sent out of theprogram as output.
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Computer programs perform the following
three steps:
1.&nut is recei'ed
2.Some rocess is er!ormed on the inut
/.,utut is roduced
2.2 &nut) Processing) and ,utut
Figure 2-/ The nput#proce$$ng# and output of
the pay calculatng program
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2./ Dis(aying ,utut "ith the print
Statement
Concept:
You use the print statementto display output in a Pythonprogram.
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2./ Dis(aying ,utut "ith the print
Statement
Strings and String iterals
• + string is a se0uence o! characters that is used as
data.
• When a string aears in the code o! a rogram) it
is ca((ed a string (itera(.
• &n Python) sing(e-0uotes 3 or doub(e-0uotes 43
can be used to enc(ose string (itera(s.
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2./ Dis(aying ,utut "ith the print
Statement
Program 2-/ %apo$trophe&py'
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2./ Dis(aying ,utut "ith the print
Statement
Program 2-5 %d$play()uote&py'
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2.5 Comments
Concept:
omments are notes of
e!planations that document linesor sections of a program.omments are part of theprogram, but the Pythoninterpreter ignores them. Theyare intended for people who maybe reading the source code.
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2.5 Comments
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2.6 7ariab(es
Concept:
" variable is a name thatrepresents a value stored in the
computer#s memory.
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2.6 7ariab(es
Figure 2-5 The age vara*le
reference$ the value 25
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2.6 7ariab(es
Program 2-8
%vara*le(demo2&py'
Figure 2-6
Two vara*le$
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2.6 7ariab(es
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2.6 7ariab(es
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2.6 7ariab(es
Tab(e 2-1 +ample vara*le name$
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2.6 7ariab(es
Program 2-9 %vara*le(demo3&py'
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2.6 7ariab(es
Program 2-1:%vara*le(demo4&py'
Figure 2-; ,ara*lerea$$gnment n
rogram 2-1"
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2.6 7ariab(es
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2.6 7ariab(es
Program 2-11 %$trng(vara*le&py'
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2.; eading &nut !rom the
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2.; eading &nut !rom the
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2.; eading &nut !rom the
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!eading Strings with the raw_input "unction
The raw_input functon retreve$ all .ey*oard nput a$ a
$trng&
2.; eading &nut !rom the
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2.= Per!orming Ca(cu(ations
Concept:
Python has numerous operatorsthat can be used to perform
mathematical calculations.
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2.= Per!orming Ca(cu(ations
Tab(e 2-2 ython math operator$
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2.= Per!orming Ca(cu(ations
Program 2-16%$ale(prce&py'
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2.= Per!orming Ca(cu(ations
For Example:num_add = 17 + 5 # the answer will be22num_div_int = 3 2 # the answer is 1! "5is the $ra%tional part # and it is trun%atednum_div_real = 3" 2" # the answer is
15
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2.= Per!orming Ca(cu(ations
1 &perations that are en%losed inparentheses
2 Exponentiation ''3 (ultipli%ation ') division ) and remainder
* ,ddition + and subtra%tion -Tab(e 2-/ +ome e/pre$$on$
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2.= Per!orming Ca(cu(ations
Tab(e 2-5 0ore e/pre$$on$ and ther value$
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2.= Per!orming Ca(cu(ations
The #$ponent and !emainder %perators>> is the exonent oerator. &ts urose is to raise a
number to a o"er.
For Exam(e#
area ? (ength>>2
@ is the remainder oerator. &ts urose is to er!orm
di'ision and return the remainder.
For Exam(e#
(e!to'er ? 1= @ / Aremainder is 2
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2.= Per!orming Ca(cu(ations
Tab(e 2-; lge*rac and programmng e/pre$$on$
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2.= Per!orming Ca(cu(ations
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2.= Per!orming Ca(cu(ations
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2.= Per!orming Ca(cu(ations
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2.8 Bore +bout Data ,utut
Tab(e 2-= +ome of ython$ e$cape character$
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2.8 Bore +bout Data ,utut
When the is used "ith t"o strings) it er!orms
string concatenation.
For Exam(e#
rint this is* one string.* A one string is aended to another
,utut#
This is one string
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2.8 Bore +bout Data ,utut
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2.8 Bore +bout Data ,utut
Figure 2-8 $ng the $trng format operator
Program 2-21 %formattng&py'
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2.8 Bore +bout Data ,utut
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2.8 Bore +bout Data ,utut
Program 2-2/ %column$&py'
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2.8 Bore +bout Data ,utut
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&'#ST(%)S
*
Chapter 2Input, Processing, and Output