Structuring Programs for Languages and Applications

1
Structuring Programs for Languages and
Applications

• Chapter 7
• Problem Solving with Loops

2
The Loop Logic Structure

• 3rd logic structure
• Repeating structure
• WHILE/WHILE-END loop
• Repeats while condition is true
• Stops when condition is false
• REPEAT/UNTIL loop
• Repeats while condition is false
• Stops when condition is true
• Automatic-counter loop

3
Incrementing (counting)

• COUNTER COUNTER 1
• or C C 1
• Used to count number of items as part of solution
  to problem

4
Accumulating (summing)

• SUM SUM VARIABLE
• or S S V
• Sum Variable must be initialized to 0 before
  starting loop
• TOTALSALES TOTALSALES SALES

5
WHILE/WHILE-END

• Repeat all instructions between WHILE and
  WHILE-END until condition is FALSE
• WHILEltCONDITION(S)gt
• INSTRUCTION
• INSTRUCTION
• .
• .
• WHILE-END

• Brackets and indention to improve readability

6
WHILE/WHILE-END Flowchart

• WHILE symbol diamond (decision)
• Circles on page connectors are used-only part
  of a flowchart

7
Example

• Page 127
• Create algorithm and flowchart to find average
  age of all students in a class.

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REPEAT/UNTIL

• Repeat instructions between REPEAT and UNTIL
  until condition is TRUE opposite of
  WHILE/WHILE-END

• REPEAT
• INSTRUCTION
• INSTRUCTION
• .
• .
• UNTIL ltCONDITION(s)gt

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REPEAT/UNTIL flowchart

• Use brackets and indentation
• Place repeat on flowchart

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WHILE/WHILE-END vs REPEAT/UNTIL

• Do not know of times instructions will be
  repeated
• Instructions in loop dont want processed
• Examples
• Entering info on clients -dont know of clients
• Total of sales-dont know how many sales
• Calculating test averages

• Do not know of times instruction will be
  executed
• Instructions WILL BE executed at least once
• Dont know condition for repeating until after
  instructions are processed

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Example

• Page 131
• Same as previous example average age of
  students in class

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Automatic-Counter

• Increments or decrements a variable each time
  loop is repeated
• Variable as counter to start counting at
  specified - increments each time loop is
  processed
• Loop repeats until counter is greater than ending
  number

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Automatic-counter

• Beginning value, ending value, increment value
• Constants
• Variables
• Expressions (calculations)

• Test to continue depending on programming
  language
• Beginning
• end

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Automatic-counter algorithm flowchart

• LOOPCOUNTERBEGIN TO END STEP S
• INSTRUCTION
• INSTRUCTION
• .
• .
• LOOP-END COUNTER

To decrement STEP is negative BEGIN must be gt
than END
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Automatic-counter-RULES

• Executes LOOP instruction counterbeginning
  number
• Executes LOOP-END increments counter
• Counter lt END number processing continues in
  loop
• Counter gt END number processing outside loop

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Example
17
Nested Loops

• Same rules (brackets, indentation, etc.)
• Inner loop doesnt have to be same as outer loop

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Indicators

• Logical variables to change processing path or
  control when loop ends
• Flags, switches, trip values
• User does not see!

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Algorithm instructions flowchart symbols page
139-140

• Decision Logic Structure
• Instructions Incrementing Accumulating
• Loop Logic Structures

• IF/THEN/ELSE
• COUNTERCOUNTER 1
• SUMSUM VARIABLE
• WHILE/WHILE-END
• REPEAT/UNTIL
• LOOPCOUNTER-BEGIN TO END STEP S
• LOOP-END COUNTER

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Recursion

• A module or function calls itself
• Condition to end MUST BE in module
• Recursive procedures faster than conventional
  loop structures

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Recursion
Factorial number 5!(5!54321) Until N1 to
end Page 143
22
Homework Assignment

• Questions 1-4 (p 141)
• Problems 1-5 (these will be flowcharts)

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End of chapter 5