COMP 110 More loops

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COMP 110More loops

• Luv Kohli
• September 15, 2008
• MWF 2-250 pm
• Sitterson 014

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Announcements

• Facebook Tech Talk tonight, 6pm, SN011
• Google info session, 6pm, SN014, tomorrow night

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Questions?
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Today in COMP 110

• do-while loops
• for loops

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Review loops

• Often you need to repeat an action in a program

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Review loops

• Loop part of a program that repeats
• Body statements being repeated
• Iteration each repetition of body
• Stopping condition

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Review Types of Loops

• while
• Safest choice
• Not always most elegant
• do-while
• Loop iterates AT LEAST once
• for
• Similar to while, but often more convenient syntax

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Review while loop

• start
• while (not enough sandwiches)
• make a sandwich
• distribute sandwiches

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Review while loop syntax

• while (boolean expression)
• statements

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Review Using a while loop

• int n 1
• while (n lt 10)
• System.out.println(n)
• n n 1

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while loop
Evaluate Boolean expression
true
false
Execute Body
End loop
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while loop

• First, evaluate Boolean expression
• If true, go into the body
• If false, do not go into the body

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Types of Loops

• while
• Safest choice
• Not always most elegant
• do-while
• Loop iterates AT LEAST once
• for
• Similar to while, but often more convenient syntax

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do-while loop

• Similar to while loop
• At least one iteration of the loop
• First execute the loop body
• Then evaluate the Boolean expression
• If true, execute the body again
• If false, quit the body

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do-while loop
Equivalent
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do-while loop syntax

• do
• statements // loop body
• while (boolean expression)
• If Boolean expression is true, repeat loop body
• Otherwise, exit loop

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Using a do-while loop

• int n 1
• do
• System.out.println(n)
• n n 1
• while (n lt 10)

Dont forget the semicolon!
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Using a do-while loop

• What if n 20?
• int n 20
• do
• System.out.println(n)
• n n 1
• while (n lt 10)

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Infinite loop

• int n 1
• do
• System.out.println(n)
• // n n 1
• while (n lt 10)

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Types of Loops

• while
• Safest choice
• Not always most elegant
• do-while
• Loop iterates AT LEAST once
• for
• Similar to while, but often more convenient syntax

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for loop

• Components of a for loop
• Initializing actions
• Boolean expression
• Loop body
• Update actions

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for loop
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for loop syntax

• for (initializing actions Boolean expression
  update actions)
• statements // loop body

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Using a for loop

• int n
• for (n 1 n lt 10 n)
• System.out.println(n)

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while loops and for loops

• int n
• for (n 1 n lt 10 n)
• System.out.println(n)

int n 1 while (n lt 10)
System.out.println(n) n n 1
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for loop initializing actions

• Only done ONCE at the beginning of the loop,
  before the Boolean expression is tested

int n for (n 1 n lt 10 n)
System.out.println(n)
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for loop update actions

• Executed at the end of every iteration
• After the loop body, but before the next Boolean
  expression evaluation

int n for (n 1 n lt 10 n)
System.out.println(n)
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Tracing a for loop
int n for (n 1 n lt 3 n)
System.out.println(n) 1 2 3
n ? n 1 n 2 n 3 n 4
Execute initializing actions Evaluate Boolean
expression Execute body Execute update actions
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Infinite loop

• int n
• for (n 1 n lt 10 n 0)
• System.out.println(n)

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Types of Loops

• while
• Safest choice
• Not always most elegant
• do-while
• Loop iterates AT LEAST once
• for
• Similar to while, but often more convenient syntax

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Wednesday

• Spend some more time with loops

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