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APS105. Repeating. Repeating. Repeat a certain number of times Do 100 pushups! Repeat until done Do pushups until you are sore! In programming these are called “loops” “for” loops: counted, repeat until count is done “while” loops: repeat while a condition is true.

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Aps105

APS105

Repeating


Repeating
Repeating

  • Repeat a certain number of times

    • Do 100 pushups!

  • Repeat until done

    • Do pushups until you are sore!

  • In programming these are called “loops”

    • “for” loops: counted, repeat until count is done

    • “while” loops: repeat while a condition is true

loops are a very common part of programs!



While loops1
While Loops

  • General form:

    while (<expression>)

    <statement>

  • Effect:

    • Evaluate expression

    • If expression is true

      • execute statement

      • goto (1)


While loop example1
While Loop Example1

  • Read ints until zero is read, then print the sum

    .


While loop example1 curt version
While Loop Example1 (curt version)

  • Read ints until zero is read, then print the sum

    .


While loop example2
While Loop Example2

  • Read ints until a negative num, then print the average

    .


Do while loops
Do-While Loops

  • “while input number is non-zero, print it and input another number”

    • Matches a “while” loop nicely

    • Note: may print zero times if first num is zero

  • “input a number, print it, repeat if non-zero

    • Note: will print at least once

    • Matchs a “do-while” loop nicely

  • do-while: general form:

    do

    <statement>

    while (<expression>);


Do while example
Do-While Example

  • Input a number until between 1 and 10

    .



For loops1
For Loops

  • General form:

    for (<expr1>; <expr2>; <expr3>)

    <statement>

  • Identical to this while loop arrangement:

    <expr1>;

    while (<expr2>)

    {

    <statement>

    <expr3>

    }


For loops cont d
For Loops (cont’d)

  • Typical use:

    for (<initialization>; <condition>; <update>)

    <statement>

  • <Initialization>

    • Executed once at the beginning

  • <condition>

    • Must be true (non-zero) to continue

  • <statement>

  • <update>

  • goto (2)


For loop example
For Loop Example

  • Print the squares of the numbers 1..10

    .


For variations locally declared counter variable
for variations: locally-declared counter variable

  • Example

    .


For variations empty initialization
for variations: empty initialization

  • Example:

    .


For variations empty update
for variations: empty update

  • Example:

    .


For variations empty condition
for variations: empty condition

  • If condition expression is empty:

    • Assumed to be true

  • Example:

    .


For variations complex expr s
for variations: complex expr’s

  • Example:

    .



Which kind of loop to use
Which Kind of Loop to Use?

  • Use for:

    • If the number of repetitions is known

  • Use while:

    • If want to test condition before doing loop body

  • Use do-while:

    • If want to do loop body then test loop condition


Loops with condition and counting
Loops with Condition AND Counting

  • Sum the first 100 squares (starting at 1), but stop if the sum passes 100000

    .


Nesting loops example1
Nesting Loops: Example1

  • Print a triangular pattern

    • Eg., if n is 5 then print:

      1

      12

      123

      1234

      12345



Nesting loops example2
Nesting Loops: Example2

  • Print a triangular pattern of stars

    • Eg., if n is 5 then print:

      *****

      ****

      ***

      **

      *



Nesting loops example3
Nesting Loops: Example3

  • Print a triangular pattern of stars

    • Eg., if n is 5 then print:

      *

      **

      ***

      ****

      *****



Another loop example
Another Loop Example

  • User inputs a digit (retry until a digit is input)

  • Then user inputs an integer

  • Print the number of occurrences of digit in int

  • Example

    User inputs digit 3

    User inputs integer 342432

    Program outputs:

    there are 2 occurrances of 3 in 342432




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