CSE 1341 Principles of Computer Science I

1
CSE 1341Principles of Computer Science I
Note Set 2
2
Semester Overview

• Functions
• Character File I/O
• Arrays
• Pointers and Dynamic Memory Allocation
• Structures/Records
• Binary File I/O

3
Today

• Divide a program into functions
• Pass data to functions by value
• Differentiate between local and global variables
• Define variables with static storage
  classifications

4
Review of Functions
5

• FUNCTION
• a collection of statements that performs a
  specific task

• Why modularize?
• To divide programs into small, manageable tasks
• To simplify programs
• To reduce code size
• Simplify modification and maintenance processes

6
4 Parts of a Function

• double square(int x)
• int result x x
• return result

7
Calling a Function

• void displayMessage()
• cout ltlt Hello from function
• ltlt dislplayMessage.\n
• int main()
• cout ltlt Hello from main\n
• displayMessage() //Function Call
• cout ltlt Back in function main\n
• return 0

8
Function Header vs Function Call
void displayMessage() ______________ displayMessag
e() _____________
9
Function Header vs Function Call

• void displayMessage()
• cout ltlt Hello from function
• ltlt dislplayMessage.\n
• int main()
• cout ltlt Hello from main\n
• displayMessage()
• cout ltlt Back in function main
• ltlt again.\n
• return 0

10
Multiple Functions

• int main()
• coutltltStart main\n
• first()
• second()
• coutltltFini main\n
• return 0

• void first()
• cout ltlt In first\n
• void second()
• cout ltlt In Second\n

Output???
11
Functions with Parameters
12
Parameters

• Parameter
• special variables that hold a value being passed
  into a function
• Argument
• Values sent to a function

int result pow (2, 4) void displayVal(int num)
13
Functions with Parameters

• void displayValue(int num)
• coutltltThe value is
• ltlt num ltlt endl
• int main()
• coutltltPassing Values\n
• displayValue(5)
• displayValue(10)
• return 0

Output???
14
Multiple Parameters
Function Name
Return Type
Parameter List

• void calc(int num1, int num2, int num3)
• int temp num1 3
• cout ltlt ( tempnum2(num32) ) ltlt endl

15
Multiple Parameters

• void calc(int num1, int num2, int num3)
• int temp num1 3
• cout ltlt ( tempnum2(num32) ) ltlt endl
• int main()
• int value1 3, value2 4, value3 5
• calc(value1, value2, value3)
• return 0

How would output change with the function
call calc(value2, value1, value3)
16
Exercise

• Write a function that prints the largest of two
  integers that are passed in as arguments.
• Write three calls to this function passing
  different data
• what are some things to think about testing?
  Special Cases?

17
Function Prototypes
18
Function Prototypes

• Function definition or function prototype must
  appear before any function call in the source
  code.
• The compiler must know the correct, legal
  format of a function call.
• It can get this info from
• Function Header
• Function Prototype

19
Prototype vs. Function Header

• Prototype
• Must have return data type
• Must have name
• Must be terminated with semi-colon
• Must have parameter data types
• May have parameter names

• Function Header
• Must have return data type
• Must have name
• Must have parameter data types
• MUST have parameter names
• Not terminated with semi-colon

Note Both must list all parameters. Prototype
must agree with the function header
20
Prototype vs. Function Header

• void showSum(int, int, int)
• int main()
• int value1 3, value2 4, value3 5
• showSum(value1, value2, value3)
• return 0
• void showSum(int num1, int num2, int num3)
• cout ltlt (num1num2num3) ltlt endl

Prototype
Function Header
21
Passing by Value
22
Passing by Value

• When an argument is passed to a function, only a
  copy of the actual argument is passed.
• Changes to a function parameter do not affect the
  original argument sent to the function.

23
Passing by Value

• void modify(int)
• int main()
• int var 3
• cout ltlt var ltlt endl
• modify(var)
• cout ltlt var ltlt endl
• return 0
• void modify(int num1)
• num1 10
• cout ltlt num1 ltlt endl

24
Pass by Value Recap.

• Passing by value NEVER changes the value of the
  original argument passed to the function.

25
Local vs. Global Variables
26
Local vs. Global Variables

• Local Variables
• Known only to the function in which it is
  declared
• Cannot be accessed outside the function

• Global Variables
• Known to all functions in the same file
• Can be known to other functions in other files
• Cannot be accessed inside a function if that
  function has a variable by the same name unless
  the scope resolution operator is used

27
Local Variables

• void anotherFunc()
• int main()
• int num 1
• cout ltlt Num is ltlt num ltlt endl
• anotherFunc()
• cout ltlt Now num is ltlt num ltlt endl
• return 0
• void anotherFunc()
• int num 20
• cout ltlt In anotherFunc, num is
• ltlt num ltlt endl

1
num
20
num
28
Local Variable Example

• void func()
• int main()
• int num 11
• coutltltIn main, num is ltlt num ltlt endl
• func()
• coutltltBack in main, num is ltlt num ltlt endl
• void func()
• int a 20
• cout ltlt In func, num is ltlt num ltlt endl

Whats wrong??
29
Global Variables

• void anotherFunction()
• coutltltIn func, num
• ltltnumltltendl
• num 50
• coutltltbut now, num
• ltltnumltltendl

• void anotherFunction()
• int num 2
• int main()
• coutltltmain, num
• ltlt num ltlt endl
• anotherFunction()
• coutltltback in main
• ltltnum ltltnum
• ltltendl
• return 0

2
num
30
Global Variables

• void anotherFunction()
• coutltltIn func, num
• ltltnumltltendl
• num 50
• coutltltbut now, num
• ltltnumltltendl

• void anotherFunction()
• int num 2
• int main()
• coutltltmain, num
• ltlt num ltlt endl
• anotherFunction()
• coutltltback in main
• ltltnum ltltnum
• ltltendl
• return 0

50
num
2
31
Global Variables

• void anotherFunction()
• coutltltIn func, num
• ltltnumltltendl
• num 50
• coutltltbut now, num
• ltltnumltltendl

• void anotherFunction()
• int num 2
• int main()
• coutltltmain, num
• ltlt num ltlt endl
• anotherFunction()
• coutltltback in main
• ltltnum ltltnum
• ltltendl
• return 0

50
num
2
32
Global Variables Whats Wrong?

• void anotherFunction()
• coutltltIn func, num
• ltltnumltltendl
• num 50
• coutltltbut now, num
• ltltnumltltendl

• include ltiostreamgt
• using namespace std
• void anotherFunction()
• int main()
• coutltltmain, num
• ltlt num ltlt endl
• anotherFunction()
• coutltltback in main
• ltltnum ltltnum
• ltltendl
• return 0
• int num 2

Access before definition
Point num is only accessible AFTER it has been
declared
33

• Problem!!
• What if you have a global variable and local
  variable that have the same name? How do you
  access one of the other?

34
Global AND Local

• int val 1
• int main()
• int val 111
• cout ltlt Local val ltlt val
• ltlt endl
• cout ltlt Global val ltlt val
• ltlt endl
• return 0

Use scope resolution operator to access global
variable
35
Storage Classifications
36
Storage Classification of Variables

• auto default type, automatic variables are the
  ones weve been using all along
• extern tells the computer that the variable is
  defined elsewhere in the program
• register tells the computer to use one of the
  CPUs registers
• static value persists (its value remains) even
  after leaving the function

37
Non-Static Local Variable

• void showLocal()
• int main()
• for(int i 0 i lt 4 i )
• showLocal()
• return 0
• void showLocal()
• int localNum 5
• cout ltlt localNum ltlt localNum
• ltltendl
• localNum 99

5 5 5 5
Will always display 5
38
Non-Static Local Variable

• void showStatic()
• int main()
• for(int i 0 i lt 4 i )
• showStatic()
• return 0
• void showStatic()
• static int localNum 5
• cout ltlt localNum ltlt localNum
• ltltendl
• localNum

5 6 7 8
Defined only once
39
Other Stuff
40
Blackboard

• Make Sure you can log in to BB
• Explore

41
Using UNIX and vi

• Connect to UNIX server using Exceed (in Lab) or
  PuTTY (outside of lab)
• UNIX vi tutorials and quizzes
• Read, comprehend, and work through the tutorials
  that are linked on outline and on Blackboard.
• Need to be completed by the end of Week 3 Lab
• Take the quizzes when you feel comfortable, but
  before end of lab for 3rd week. Quiz link will
  go away.
• Quizzes are password protected have TA type in
  PW for you

42
Using UNIX

• Many UNIX Servers to choose from
• apoc
• tank
• janus
• Access using Exceed from in Lab
• Access using (from outside SOE Lab)
• PuTTY (ssh mode for off campus)

43
PuTTY

• Excellent way to login to UNIX
• To Download
• Google for putty
• Choose second link PuTTY Download Page

44
PuTTY
45
UNIX and vi

• Tutorials available at
• http//www.ee.surrey.ac.uk/Teaching/Unix
• http//heather.cs.ucdavis.edu/matloff/UnixAndC/Ed
  itors/ViIntro.html

46
Questions?
?