Lab Session-VI CSIT-120 Fall 2000

1
Lab Session-VI CSIT-120 Fall 2000

• Let us look at C syntax rules in brief
• Next, we complete the lab session-V
• Lab session-VI deals with functions (OPTIONAL)
• We will learn how to write independent functions
  that can be called from main()
• We do not use parameter passing, however, we
  learn how functions can return values
• Lab VI Continues (FINAL SESSION)

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

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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

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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

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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)

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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
The for Statement

• for is a loop statement that is controlled
  through a loop control variable
• for (lcv1 lcvlt100 lcv)
• The above loop will start with lcv1 and it will
  run until lcv equals 100. The step size is 1
  (lcv)
• Compare it to the above
• for (lcv1 lcvlt100 lcv2)

9
The for Statement

• for statement and while statement can produce
  identical loops
• for is preferred if the number of iterations is
  known beforehand. while is preferred if the
  total iterations cannot be computed in advance

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Logical Operators

• Logical AND is represented by
• Logical OR is represented by
• Logical NOT is represented by !
• Comparing if equal is represented by
• Example Write a logical expression to be true if
  x is restricted between 1 and 100
• Write a logical expression to check if x equals
• y-50 and x is positive
• Experiment 5.5

11
Lab Exercise

• 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,..

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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

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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.

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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

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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

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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)

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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

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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().?

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Lab VI Continued

• We look at some C code segments
• We solve one programming problem
• Lab Assignment5 due 12/7

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Basic Concepts

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

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Basic Concepts

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

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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

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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--

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Basic Concepts

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

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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..

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Lab Assignment5 Due 12/7

• A car can hold 12 gallons of gasoline and it can
  travel 360 miles without refuelling. Write a
  program the displays the trip meter of the car
  followed by amount of fuel left. Every time the
  user enters letter r, 10 miles are added to the
  trip meter and appropriate amount of fuel is
  deducted. As the amount of fuel becomes 1 gallon,
  the program prints a warning.

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Sample Output

• s
• Miles so far 160 Fuel left 6.66667
• s
• Miles so far 160 Fuel left 6.66667
• r
• Miles so far 170 Fuel left 6.33333
• r
• Miles so far 180 Fuel left 6