Functions II It just wont leave

1
Chapter 9,10

• Functions II It just wont leave!!!

2
Functions

• We have discussed value-return and void functions
• The last type of function we will cover is a type
  of void function that data can be sent back and
  forth

3
Void Functions

• In the void function, the data that is being sent
  is stored in the parameter of the function.
• void print_value(int i)
• The parameter is in between the open and closed
  ().
• Parameters
• Value Parameters
• Reference Parameters

4
Void Functions

• There are two types of parameters
• Value Parameters
• Reference Parameters

5
Value Parameters

• When you pass a variable to a function by value,
  a copy of the value in the variable is given to
  the function for it to use.
• If the variable is changed within the function,
  the original copy of the variable in the calling
  function remains the same.

6
Value Parameters Example
7

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

8

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

9
Comment lines and Libraries
10

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

11
Declaring a Function

• void print_value(int i)
• Remember If a function starts with anything
  other then the word void, it is a value returning
  fuction.
• In this function, a variable called i with the
  data type int is being created.
• The variable i is being sent from the main
  function to the print_value function

12

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

13

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

14
Declaring the i variable
15

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

16
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17

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

18
Function call
19

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

20

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

21
(No Transcript)
22

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

23

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

24
(No Transcript)
25

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt "The value after the function exits is
  " ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

26
(No Transcript)
27
Remember

• In a value parameter, only a copy of the variable
  is being sent. The original value of i is not
  effected in the main function

28

• // passval.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt "The value before the function is " ltlt
  i ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt "The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltlt i ltltendl

29
End of the program
30
Reference Parameters

• Functions that pass variables by reference will
  pass any changes you make to the variables back
  to the calling function.
• To pass a variable by reference, simply precede
  the variable name with an ampersand () in the
  function definition.

31

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

32

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

33
Comment lines and Libraries
34

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

35
Declaring a Function

• void print_value(int i)
• Remember If a function starts with anything
  other then the word void, it is a value returning
  fuction.
• In this function, a variable called i with the
  data type int is being created.
• The variable i is being sent from the main
  function to the print_value function

36

• Tells the compiler that the parameter is a
  reference parameter

37

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

38
Main Function
39

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

40
Declaring the i variable
41

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

42
(No Transcript)
43

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

44
Function call
45

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

46
(No Transcript)
47

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

48

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

49
(No Transcript)
50

• // passref.cpp
• include ltiostreamgt
• using namespace std
• void print_value(int i) // function prototype
• int main()
• int i 2
• cout ltlt"The value before the function is " ltlt i
  ltlt endl
• print_value(i)
• cout ltlt"The value after the function exits is "
  ltlt i ltlt endl
• return 0
• void print_value(int i)
• cout ltlt"The value passed to the function is "
  ltlt i ltlt endl
• i i 2 // the value in the variable i is
  doubled
• cout ltlt"The value at the end of the function is
  "ltltiltltendl

51
(No Transcript)
52
Remember

• In a reference parameter, any changes to the i
  variable will change the variable in the main
  function