Transcript BACS 287 - University of Northern Colorado

BACS 287
Programming
Logic 3
BACS 287
Iteration Constructs

Iteration constructs are used when you want
to execute a segment of code several times.

In pseudocode there are 2 different iteration
types:
–
DO WHILE - Test at top, 0 or more loops
–
DO UNTIL - Test at bottom, 1 or more loops
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Do While Structure
DO WHILE condition
action 1
...
action n
ENDDO

This executes while the condition continues
to be true
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Do While Example 1
Get positive Value from user
DOWHILE Value < 0
Print “Error, enter a positive value”
Get positive Value from user
ENDDO
Print Value
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Do While Example 2
sum = 0
cnt = 0
Display “Enter test score OR -999 to exit”
Read input
Do While input <> -999
sum = sum + input
cnt = cnt + 1
Read input
End Do
avg = sum / cnt
<-- why is this line a problem?
Print avg
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Do Until Structure
DO UNTIL condition
action 1
...
action n
ENDDO

This executes as long as the condition is not
met
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Do Until Example 1
Read system password
DOUNTIL user password correct
Get password from user
ENDDO
...
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Do Until Example 2
num = 0
Read system password
DOUNTIL user password correct OR num = 3
Get password from user
num = num + 1
ENDDO
If num = 3 then
<-- why is this ‘IF’ a problem?
print “Sorry - Too many tries”
Exit Program
EndIf
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Comparison of Iteration Structures
Do While Structure
cnt = 1
Do While cnt < 11
Print cnt
cnt = cnt + 1
End Do

Do Until Structure
cnt = 1
Do Until cnt > 10
Print cnt
cnt = cnt + 1
End Do

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How Do Iteration
Structures Work?

Do While Structure
cnt = 1
Top: If cnt > 10 then
goto End
EndIf
Print cnt
cnt = cnt + 1
goto Top
End:

Do Until Structure
cnt = 1
Top: Print cnt
cnt = cnt + 1
If cnt < 11 then
goto Top
EndIf
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Comparison of Iteration Structures
Do While Structure
Read input record
Do While Not EOF
Gross = Hours * Rate
Print Gross
Read input record
End Do
Print Summary

Do Until Structure
Read input record
Do Until EOF
Gross = Hours * Rate
Print Gross
Read input record
End Do
Print Summary

What if the input file is empty?
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Iteration and Selection
Read input record
Do While Not EOF
If Balance < 0 then
Print “Overdrawn Account”
EndIf
Read input Record
EndDo
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Iteration Problem 1

Write pseudocode to print “HI MOM” 100
times.
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Iteration Solution 1
cnt = 1
Do While cnt < 101
Print “HI MOM”
cnt = cnt + 1
End Do
cnt = 1
Do Until cnt > 100
Print “HI MOM”
cnt = cnt + 1
End Do
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Iteration Problem 2

Write the pseudocode to play a simple
“guess the secret number” game. The user
has 10 tries to guess. No hints are given
after each guess.
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Iteration Solution 2
Generate random secret-number
cnt = 0
Do Until Guess = secret-number OR cnt = 10
Print “Input your guess”
Read Guess
cnt = cnt + 1
End Do
If Guess = secret-number then
Print “Congratulations!!
Endif
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Iteration Problem 2a

Modify the previous problem to give the
player hints of “Too high” or “Too low” during
the game. The user still has 10 tries to
guess.
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Iteration Solution 2a
Generate random secret-number
cnt = 0
Do Until Guess = secret-number OR cnt = 10
Print “Input your guess”
Read Guess
If Guess < secret-number then
Print “Too Low”
Elseif Guess > secret-number then
Print “Too High”
EndIf
cnt = cnt + 1
End Do
If Guess = secret-number then
Print “Congratulations!!
Endif
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Iteration Problem 3

Sum the odd numbers between 1 and 100
and print the results.
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Iteration Solution 3
sum = 0
cnt = 1
Do While cnt < 100
sum = sum + cnt
cnt = cnt + 2
End Do
Print sum
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Iteration Problem 4

Ask the user for a starting positive number.
Continuing asking until they enter a valid
number. Next, print the numbers from this
starting number to 0.
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Iteration Solution 4
Start
Ask user for start-num
DoWhile start-num <= 0
display error message
Ask user for start-num
End Do
Do While start-num >= 0
Print start-num
start-num = start-num - 1
End Do
End
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