for Loops and Functions

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for Loops and Functions

• Making things easier

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while

• Called a pretest loop
• initialize getting started
• while (condition)
• one or more instructions
• increment

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Example

• i -20
• while ( i lt40)
• ..
• i i 1

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Example

• fileIN gtgt a
• while ( !fileIN.eof())
• instructions
• fileIN gtgt a

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For loop

• for ( k 1 k lt 10 k)
• cout ltlt k ltlt
• j kk
• cout ltlt jltltendl

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Basic form of the for

• for(initial value final value increment)
• instructions

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Note The following are often used as increments
but commands like x x 3 or y y 0.1 can
also be used

• k
• k
• k - -
• - - k

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Mystery

• A mathematician is the only witness to a crime
  and sees the license plate of the get-away car.
  The license is all numeric and of the form
  xx-yy-zz. The mathematician only remembers that
  the license plate satisfied the Pythagorean
  theorem and xx, yy, and zz are all 10 or more.
  Display a list of possible license plates.

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Solution hint

• The easiest way to do this is with a triple
  nested loop.
• for (i 10 i lt 100 i) for ( j 10 j lt
  100 j) for (k 10 k lt 100 k)
• ..

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Post test loops - do while

• do
• instructions
• while (condition)

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Note

• The do while and the for instructions can be
  replicated using only the while.
• These are often used to make coding easier.
• A similar relation exits between ifelse and
  switch.

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functions

• A functions is a reusable block of code that can
  be shared.
• A function is a box that has input (called
  parameters) and at most one well defined output.
• The data type of the parameters and output must
  be known to use a function properly.
• You can use functions to breakup a program into
  smaller, easier to code modules.

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A function prototype

• A function prototype tells you about the data
  type of the input and output.

Input Output
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Function Prototypes in C

• Basic prototype
• outputDataType functionName ( inputDatatype1
  dummyVariable1, )
• examples
• double pow(double a, double b)
• void main (void)
• int product ( int a, int b)
• Note prototypes are terminated with

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Write prototype statements for the following
functions

• Display only your name on the screen
• void myNamePrint (void)
• Find the area of a circle given the radius
• double circleArea (double radius)
• Find the first non-zero digit of a student_id.
• int firstDigit (long id)
• Display the largest of 3 integers
• void printBiggest ( int a, int b, int b)

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Find the error in the following prototypes

• int funOne ( double x, float y)
• no ending
• void funTwo (void, void)
• Can not use void, void. Just use void.
• float funThree( float x, y)
• each dummy variable must have its own data type.

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Corrected prototypes

• int funOne ( double x, float y)
• void funTwo (void)
• float funThree( float x, float y)
• Proper C prototype. Though java an C use dummy
  variable C actually just uses the only data
  type in the prototype. However all work
  correctly.
• int funOne(double, double)
• float funThree (float, float)

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A function definition or how to build your own

• int product (int x, int y)
• int t
• t x
• t t y
• return t

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Some comments

• A function consists of
• the header which is similar to the prototype
  statement with no
• The function body
• return
• variables or parameters are never defined (x and
  y in this case)
• other variable, like t, are called local
  variables.

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More comments

• local variables can not be seen outside the
  function in which they are defined
• in this example the parameters are passed by
  value and can NOT be changed.
• there can only be one function called main

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Another look at product

• // A function definition or how it works
• int product (int x, int y)
• int t
• t x
• t t y
• return t

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Find the error in the following

• void fun (int x, int y)
• int z
• z xx 2xy yy
• return z

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Your own function in a C program

• A function consists of two parts.
• the function prototype
• the function definition
• Common location in source code
• include
• one or more function prototypes
• main
• one or more function definitions

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Using a function

• Use the defined functions as you would any other
  function (like y sqrt(x), y sin(x))

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• include ltiostreamgt
• using namespace std
• int product (int x, int y)
• void main (void)
• int a, b, c
• a 10
• b 20
• c product (a,b)
• cout ltlt cltlt endl
• getchar()
• return
• int product (int x, int y)
• int t
• t x
• t ty
• return t