Lab Session-VI CSIT-120 Spring 2001

1
Lab Session-VI CSIT-120 Spring 2001

• Let us look at C syntax rules in brief
• Exercise VI-A (Demo Required)
• Lab Assignment4 Due May 1st, 2001
• (No Lab on April 24th, .To Earthquake Zone)
• Lab session-VI deals with functions
• We will learn how to write independent functions
  that can be called from main()
• Students are given examples of functions

2
C Syntax Rules in Brief

• include ltiostream.hgt
• ..other include files go here
• void main(void)
• Declarations of variables and constants
• Assignment and control statements

3
C Syntax Rules in Brief

• Make it a habit to put declarations in the
  beginning. For example,
• int employeeID
• const int current-year2000
• float deduction-amount
• Once a data item has been declared, do not
  mention its data type in assignment statement
• int employeeID23 is WRONG
• employeeID23 is RIGHT

4
C Syntax Rules in Brief

• If you write a control statement, its conditions
  must be in parenthesis with no semicolon after
  the parenthesis
• For example, displaying employeeID if employeeID
  is 24
• if (employeeID 24)
• coutltltID is ltltemployeeIDltltendl
• Please note double-equal in comparing, no
  semicolon after comparison statement and joining
  several displayable messages with ltlt

5
C Syntax Rules in Brief

• Different comparison statements
• if (employeeID ! 24) coutltltendl
• (if employeeID is not equal to 24, do a blank
  cout)
• if (employeeID gt 24)
• if (employeeID lt24)
• if (employeeID gt 24)
• if (employeeID lt 24)
• We could also use an else clause to capture the
  false results of comparison

6
C Syntax Rules in Brief

• For example, if employeeID is 24, display ID is
  24 else do a blank line display
• if (employeeID 24)
• coutltltID is ltltemployeeIDltltendl
• else coutltltendl
• Use braces to show blocks of code even if only a
  single statement is there in if part or else part
  (for clarity purposes)

7
C Syntax Rules in Brief

• In assigning values, there can be only one
  destination shown on left of the single equal
  sign
• deductions pay- (paytax-percentage)
• Please note the use of parenthesis to emphasize
  and make the expression very clear

8
Lab Exercise VI-A

• Develop a program that takes a number from the
  user and then enters a loop to keep displaying
  the result of successively multiplying the number
  by 2. The loop is terminated when the number
  exceeds half of INT_MAX (Do not forget to include
  the header file limits.h)
• Example 2,4,8,16,32,64,..

9
Lab Assignment4 Due 5/1

• A classroom has the maximum capacity of 37
  people, write a program that accepts the total
  number of students wishing to register for a
  course. This program checks for any violations of
  fire safety code. It asks the user to input the
  total number of students. If this number is more
  than the maximum allowed, it prints a warning and
  shows how many people will not get the course
  otherwise it shows the additional number of
  people who can be admitted to the course. Bonus 2
  marks for making it a loop and asking again and
  again until the number of students is exactly
  equal to the capacity

10
Lab VI Continued

• We look at some C code segments
• Introducing functions
• We solve one programming problem

11
Basic Concepts

• What will be the output? Dont run this code,
  just predict
• void main()
• int num1,num2
• num112345 num26789
• coutltltnum1ltltnum2ltltendl

12
Basic Concepts

• What is wrong with this code segment?
• void main()
• int num1, myloop
• while (mylooplt24)
• coutltltOnce in myloop, show no mercyltltendl

13
Basic Concepts

• What is wrong with this code segment?
• Void main()
• int mybirthdate
• mybirthdate 2
• while (mybirthdatelt24)
• coutltltEnter my birth date (date only)ltltendl
• cingtgt mybirthdate
• coutltltyou got it\n

14
Basic Concepts

• What is the error in this code segment?
• int cans
• for(int cans1 canslt100 cans)
• coutltltEach one has a refund of 5 cents\n
• coutltltcount until 100 cans are done
• cans--

15
Basic Concepts

• Fix this code segment
• int k
• coutltltNumber please cingtgtk
• if (k5) coutltltYou typed 5
• else coutltltNothing else please

16
Functions

• Functions are subroutines, procedures,
  modules or program units.
• Functions perform a given task, usually one
  function is dedicated to one task
• One advantage of using functions is to avoid
  repeated coding for the same job

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Functions Reduce Code Size

• For example, consider a program that prints text
  in a box, something like below
• 
  
• The Journey Through Central Spine
  
• 
  
• We can achieve this printout with a program
  containing 9 cout statements OR we can develop a
  function to print aesterik lines

18
Program with 9 cout Lines

• coutltltltlt
  endl
• coutltltltlt
  endl
• coutltltltlt
  endl
• coutltlt
  ltltendl
• coutltlt The Journey Through Central Spine
  ltltendl
• coutltlt
  ltltendl
• coutltltltlt
  endl
• coutltltltlt
  endl
• coutltltltlt
  endl.

19
Same Program with a Function

• Print_three_star_lines()
• coutltlt
  ltltendl
• coutltlt The Journey Through Central Spine
  ltltendl
• coutltlt
  ltltendl
• Print_three_star_lines()
• Now the program is more compact and readable.
  Actual function definition will be developed
  after the main() functions code
• DEMONSTRATION OF PROGRAM

20
Function Specific Actions

• If you plan to work with functions, make sure
  that you name your functions according to C
  naming conventions
• (letters, underscores, digits, no digits in the
  beginning)
• As demonstrated, function data type is specified
  before its name. If the function does not return
  anything, void is used
• Also note the DECLARATION before the actual
  function code, ending with a

21
Function Call

• Notice the function name is simply repeated when
  it is called from the main routine
• print_three_star_lines()
• The empty parenthesis indicate the fact that no
  data is passed to this function. A semicolon is a
  must to terminate any C statement (except loop
  starters)

22
The Events

• When a function is called from the main routine,
  the following events take place
• Control (of the running program) is transferred
  to the function as well as any data that may be
  needed
• Function performs its task and at the end,
  transfers the control back to the calling routine

23
Why does the Function name appear so many times?

• Count the number of times the function name is
  repeated in our program
• The name appears each time for a different
  purpose
• Firstly we have to declare the function. Function
  declaration is called its prototype
• void print_three_star_lines()

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Why does the Function name appear so many times?

• Next, we have to define the function,i.e. its
  actual source code
• void print_three_star_lines() .
• Finally, we have to make the function call
• print_three_star_lines()
• What do you know about main function when it
  reads void main().?

25
Lab Programming Exercise

• Write a program that accepts a digit entered by a
  user and then displays it in words.
• For example, user enters 8, program displays,
  You Entered Eight
• User enters 0, program displays You Entered
  Zero
• and so on..