CSC115 Introduction to Computer Programming

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CSC115 Introduction to Computer Programming

• Zhen Jiang
• Dept. of Computer Science
• West Chester University
• West Chester, PA 19383
• zjiang_at_wcupa.edu

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Table of Contents

• Structure
• Selection (Decision)
• Loop
• Array and Function

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Selection (Decision)

• Price is right.
• Sample execution (click on this link to try)

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No
Yes
Condition
Action 1
Action 2
Action 3
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Yes
No
Boolean Expression
Action 1 If controlled
Action 2 else controlled
Action 3
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• If block
• if condition then
• action 1 (statements 1)
• else
• action 2 (statements 2)
• end if
• action 3 (statement 3)

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• Legal age to have drivers license

?
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• Condition
• Simple condition
• Format
• ltValuegt ltrelational operatorsgt ltValuegt
• Number value relational operators
• , ltgt, lt, gt, lt, gt
• String value relational operators
• , ltgt
• Complex condition
• And, or, not
• Truth table, table 4, p121

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• Relational operators have lower precedence than
  math operators.
• (7 - 1) 5 3 gt 7 5
• 6 5 3 gt 35
• 30 3 gt 35
• 33 gt 35
• False
• Relational operators cannot be chained (unlike
  math operators)
• 2 lt x lt 10
• error!

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Development Process

• Identify two exclusive options
• Implement each handling in different action parts
• Identify the situation (values) for option
  selection
• Make a condition so that all the situation value
  for option part 1 will lead to this condition
  true.
• Verify all the situation value for option part 2
  will lead to this condition false, otherwise,
  revise the above condition!

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• Multiple selection
• Nested if block
• Example letter grade

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• Comments
• Nested if block for multiple section problem
• If then
• case 1
• Else
• if then
• case 2
• else
• end if
• End if

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• If block, extension without else
• if condition then
• action 1 (statements 1)
• end if
• action 3 (statement 3)

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Are they different, how much?
Dim x as integer, y as integer x
text1.text y0 if x gt 3 then y 1 if x gt10
then y 2 else y 3 End if End
if Listbox1.Items.Add( y )
Dim x as integer, y as integer x
text1.text y0 if x gt 3 then y 1 if x gt 10
then y 2 End if else y 3 End
if Listbox1.Items.Add( y )
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Try 0, 4, 11 and see the results!
Dim x as integer, y as integer x
text1.text y0 if x gt 3 then y 1 if x gt10
then y 2 else y 3 End if End
if Listbox1.Items.Add( y )
Dim x as integer, y as integer x
text1.text y0 if x gt 3 then y 1 if x gt 10
then y 2 End if else y 3 End
if Listbox1.Items.Add( y )
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Try 0, 4, 11 and see a worse situation!
Dim x as integer, y as integer x
text1.text y0 if x gt 3 then y 1 if x lt10
then y 2 else y 3 End if End
if Listbox1.Items.Add( y )
Dim x as integer, y as integer x
text1.text y0 if x gt 3 then y 1 if x lt 10
then y 2 End if else y 3 End
if Listbox1.Items.Add( y )
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• My point
• One line in wrong place
• Could create the program 99.99 different
• Structural procedure
• Ask yourself where (the next program segment
  line) the computer execution goes
• Before that, ask yourself if you can find the
  if for each else
• Ex 6

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• Select block
• Select case
• A constant
• A variable
• An expression
• Is
• To range
• Else
• And and or

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Loop

• Do while Loop
• do while condition
• statements
• loop
• statements2

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No
Yes
condition
statements1
Action 2
Action 3
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No
Yes
condition
Statements1
Statements2
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• Other loops

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• Clock

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• Function and procedure

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• Array