Functions

1
Functions

• Data Flow
• Scope local global
• part 4

2
Data Flow

• Data flow is the direction of the information
  flow between the function and its caller.
• Adding data flow documentation to the function
  interface is helpful.
• The flow could be into a function, out of a
  function or both.

3
Parameter and Data Flow

• pass data into a function / in /
• pass data out of a function / out /
• pass data into and out of a function / inout
  /

4
Parameter and Data Flow

• Examples
• void myFunction( / in / double nana,
  / in / int count)
• void yourFunction( / out / int num1,
  / out / int num2)
• void ourFunction( / in / int alpha,
  / inout / int beta)

5
Parameter and Data Flow

• To be certain a function does what you want it to
  do, write value of variables as you enter and
  exit a function.
• Put the output statement into a function and call
  it whenever you need it.

void ShowIt(void) coutltlt var1ltlt \t
ltltvar2ltlt \t ltltvar3ltlt \n

6
Data Flow - Example

• includeltiostreamgt
• using namespace std
• void getTemp(double)
• void activity(double)
• void convertCtoF(double)
• void main(void)
• double temperature
• getTemp(temperature)
• activity(temperature)

7
Data Flow - Example
out

• void getTemp(/ / double temp)
• coutltlt"Enter the temperature in degrees C "
• cingtgt temp
• coutltlt"The current temperature is "
• ltlttempltlt" degrees celsius."ltltendl
• convertCtoF(temp)
• void convertCtoF( / / double temp)
• temp(1.8)temp 32
• coutltlt"This equals "ltlttemp
• ltlt" degrees Fahrenheit."ltltendl

inout

8
Data Flow - Example
in

• void activity(/ / double temp)
• coutltlt"The recommended activity is "
• if(tempgt85)
• coutltlt"swimming."ltltendl
• else if(tempgt70)
• coutltlt"tennis."ltltendl
• else if(tempgt35)
• coutltlt"golf."ltltendl
• else if(tempgt10)
• coutltlt"skiing."ltltendl
• else
• coutltlt"dancing."ltltendl

9
Scope

• A function is like a black boxYou know what
  goes in and what comes out, but you do not know
  what happens inside the box.

10
Scope

• The section of the program where the variable is
  valid (known or visible).
• local available to only one functionor block.
  Used to limit access.
• global available multiple functions or blocks.
  Used to save call time or reduce complexity of
  call sequence

11
Scope
Block

• LocalThe scope of an identifier declared inside
  a block extends from the point of declaration to
  the end of that block.
• GlobalThe scope of an identifier declared
  outside all functions and classes extends from
  the point of declaration to the end of the source
  file.

12
Local Variables

• declared within a function definition
• private to a function definition
• variables in different functions are totally
  independent
• different functions can have variables with the
  same names however, each variable will have its
  own memory address
• actually applies to any block

13

• int x 3 // global because before main
• void main(void)
• // no variables local to main( )
• void myfunction( ) // prototype
• cout ltlt"x "ltltxltlt" before the function
  call.\n"
• myfunction( )
• cout ltlt"x "ltltxltlt" after the function
  call.\n"
• void myfunction( )
• int r // local to myfunction( )
• r x
• cout ltlt"r "ltltrltlt" within the function.\n"

// what happens to global x?
14
Scope

• OUTPUT
• x 3 before the function call.
• r 4 within the function.
• x 4 after the function call.

15
Example - ReadValues
1. 2. 3. 4. 5. 6. 7. 8. 9.

• void main(void)
• int a, b, c float avg
• void ReadValues( int, int, int )
• void Adjust( int, int, int )
• float Average( int, int, int )
• void WriteResults( int, int, int, int, float
  )
• ReadValues(a, b, c)
• Adjust(a, b, c)
• avg Average(a, b, c)
• WriteResults(a, b, c, a b c, avg)

16
Example - ReadValues

• 1. main declares and calls ReadValues
• 2. ReadValues declares and calls ReadOne 3x
• 3. main declares and calls Adjust
• 4. main declares and calls Average
• 5. main declares and calls WriteResults

17
Example - ReadValues

• void ReadValues( / / int x, /
  / int y,
• / / int z )
• void ReadOne( char, int )
• ReadOne('1', x )
• ReadOne('2', y )
• ReadOne('3', z )
• return

out

18
Example - ReadOne

• void ReadOne( / / char number,
• / / int item )
• cout ltlt "Enter value " ltlt number ltlt " "
• cin gtgt item
• return

in
out

19
Example - Adjust
inout

• void Adjust( / / int i, /
  / int j,
• / / int k )
• int smallest
• smallest i
• if (j lt smallest) i i - smallest
• smallest j j j - smallest
• if (k lt smallest) k k - smallest
• smallest k return

20
Example - Average

• float Average( / / int item1, / / int
  item2,
• / / int item3 )
• int total
• total item1 item2 item3
• return float(total) / 3

in

21
Example - WriteResults

• void WriteResults( / / int item1,
• / / int item2, /
  / int item3,
• / / int total, /
  / float average )
• cout ltlt "Adjusted values " ltlt item1 ltlt ", "
• ltlt item2 ltlt ", " ltlt item3 ltlt '\n'
• ltlt "Sum " ltlt total
• ltlt " Average " ltlt average ltlt '\n'
• return

in

22
Main
ReadValues
Adjust
Average
WriteResults
Enter value 1 23 Enter value 2 56 Enter value
3 78 Adjusted values 0, 33, 55 Sum 88
Average 29.3333
ReadOne
23
Common Errors

• Wrong positioning of the called function
  prototype
• Terminating a function header with a
• Forgetting the data type of a functions
  parameter
• Remember the NOT rule
• Number
• Order
• Type