QMCS 230: Today in Class

1
QMCS 230 Today in Class

• More Loops
• Do While a trailing decision loop
• For loop for doing a sequence
• Accumulation, Sentinel values
• Tomorrow lab using a count controlled loop

2
Recap Parts of a Program

• The Envelope
• Class definition, Main definition
• Well just use them as patterns for now
• Variable declarations
• First thing in Main
• First part of setting up your program to run
• Some variables are initialized, not necessarily
  all of them
• Each has a comment explaining its purpose
• Executable Statements
• BLANK LINE separates them from variable
  declarations
• These are things that run when your program
  runs
• Clusters of 2-5 with a comment at the start of
  each cluster
• Indentation of Ifs and Loops

3
Parts of a loop

• Statements OutsideThe Test condition
• Statements Inside
• More Statements Outside

4
Do While

• A Trailing Decision Loop
• do
• statements to execute
• while (condition-remains-true)
• Loop statements are performed once
• Then repeated as long as the condition remains
  true

5
Leading vs Trailing decision

• Error messages and input loops
• Read input
• If error, repeat
• Print error message
• Prompt for another input
• Repeat
• Prompt for input, giving rules
• Read input
• Until input is valid

6
The For Loop

• Count controlled loop
• Used to apply a set of operations a fixed number
  of times
• Traditionally applied to lists and arrays
• (we havent studied those yet)
• for (initial-stmt test-stmt update-stmt)
• statements to perform
• Usually the loop header has a variable that
  indicates which iteration you are on

7
Accumulating Results

• We already did that in the Payroll example
• The idea repeating an operation several times,
• Accumulating partial results as you proceed

8
Sentinel Values

• Example program that averages a bunch of
  positive numbers
• Input collects one number at a time
• Once a negative number arrives, average the
  previously collected ones

9
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