Announcements

1
Announcements

• Homework 1 due Wednesday 1900
• No new homework this week, but there will be
  recitations
• About HW1
• There must be three inputs only
• First one is the amount of money
• Second one is the item name
• Third one is the item price
• You have to preserve this order
• No other inputs are allowed
• Otherwise, our system cannot process your
  homework

2
Tapestry Chapter 3

• We discussed some parts
• cin for input
• variables and basic types
• We will go over them
• More details
• More types
• Arithmetic operators and expression evaluation
  rules
• More on assignment operator (chapter 4.1 and
  4.3.4)

3
Programs that Respond to Input

• Programs without input always give the same
  results
• values are hardcoded
• For new values
• change the program, compile and run again
• not a good programming practice
• Allow the user to input values that generate
  output
• from keyboard, using cin
• we did this in the first circle area calculation
  program
• Sequential model of programming input, process,
  output
• Input information provided from the user
  (outside world)
• Process Information is processed
• Output display the result

4
Mac Donalds farm revisited

• We want the user to enter/input values for animal
  and noise
• Enter the name of an animal sheep
• Enter noise that a sheep makes baah
• Old MacDonald had a farm, Ee-igh, Ee-igh, oh!
• And on his farm he had a sheep, Ee-igh, ee-igh,
  oh!
• With a baah baah here
• And a baah baah there
• Here a baah, there a baah, everywhere a baah baah
• Old MacDonald had a farm, Ee-igh, Ee-igh, oh!
• Well pass the user-entered values to the Verse
  function
• The input stream cin takes input from the
  keyboard using operator gtgt
• Values that are input are stored in variables and
  then passed to function verse as arguments
• see macinput2.cpp

5
Mac Donalds farm revisited

• // other functions goes here (see macinput2.cpp)
• void Verse(string animal, string noise)
• // this function doesnt change
• // see the source code for the function code
• int main()
• string animal // variable for name of
  animal
• string noise // variable for noise it
  makes
• cout ltlt "Enter the name of an animal "
• cin gtgt animal
• cout ltlt "Enter noise that a " ltlt animal ltlt "
  makes "
• cin gtgt noise
• Verse(animal,noise)
• return 0

6
Analysis of the Run

1. input value sheep is stored in variable animal
2. input value baah is stored in variable noise
3. sheep and baah values are passed to function
   verse as arguments as well as used in cout in
   main

7
Variables (review from previous lectures)

• Variables are used to store values in memory
• memory locations that are accessed using a name
  in the program
• Each variable has a type, a name (identifier),
  and a value
• Methods to give values to variables
• Assignment, using
• Input, using cin
• Definition
• type variable_names_separated_by
  _comma

8
Where to define variables

• You can define variables anywhere within a
  function
• provided that it is defined before the first use
• Two common conventions the place of variable
  definition
• At the beginning of the function in which theyre
  used
• string animal,noise
• cout ltlt "enter animal "
• cin gtgt animal
• cout ltlt "enter noise a " ltlt animal ltlt " makes
  "
• cin gtgt noise
• Just before the first place that theyre used
• cout ltlt "enter animal "
• string animal
• cin gtgt animal
• cout ltlt "enter noise a " ltlt animal ltlt " makes
  "
• string noise
• cin gtgt noise

9
Where to define variables

• NO GLOBAL VARIABLES
• A global variable is a variable defined outside
  the function bodies
• They can be used in all functions without
  definition
• That is why it is the 1 enemy of parameters
• If you use global variables, you violate the
  independence property of functions and may lose
  your control in big programs
• Thus, IT IS FORBIDDEN TO USE GLOBAL VARIABLES
• If you use a global variable in hw and exams,
  your grade will be reduced!
• At the end of the course, I will formally teach
  global variable concept. After that,
• you will need to know what global variable is and
  apply them whenever you are asked for, but not
  without permission!

10
Variable Initialization

• Variables have garbage (junk values) until
• they are assigned a value using assignment
  operator or
• an input is stored into them (using cin
  statement)
• Variables must be given a value before you refer
  to its value for the first time in an expression
  or an output statement or as an argument to a
  function
• idea behind this rule you can never know what is
  inside of an uninitialized variable!
• not a syntax error, compiler may or may not warn
  you!
• You may initialize variables at the declaration
• int myint 5
• After initialization, you may change the value
  stored in a variable several times
• that is why they are named as variable

11
Scope of a Variable and Parameter

• Not explained in the book in this way
• Complex rules. Now I give a simple version!
• RULE 1 A variable or parameter can be referred
  only within the function in which it is declared
• e.g. you cannot refer the variable animal in
  function eieio
• RULE 2 A specific identifier can be used several
  times in different functions as variable or
  parameter names. Those are actually different
  variables/parameters.
• e.g. animal and noise are used both in main and
  verse
• RULE 3 A specific identifier must be unique
  within a function
• Detailed scope rules will be given later in this
  course

12
Data Types

• string
• talked on that
• more technically, string is a class
• char
• for single character
• digits, letters, symbols
• uses up one byte
• range 0 ... 255
• why? one byte (8 bits) can store 28 256
  different values.
• stores the code of the character
• e.g. 65 for A
• character arithmetic is possible (will see later)
• char literals are in single quotes (strings are
  in double quotes)
• 'z' 'T' '4' ''
• bool
• boolean (will see later)

13
Numeric Types

• to represent integer and real numbers
• int
• integer numbers
• sorry! no infinity in computers ?
• limited range
• 2 or 4 bytes (16 or 32 bits) depending on the
  computer and compiler you use
• in our case 4 bytes (32 bits)
• integer range
• 32,768 ... 32,767 for 16-bit computers
• why?
• 2,147,483,648 ... 2,147,483,647 for 32-bit
  computers
• why?

14
Numeric Types (contd)

• short int (or just short )
• always 16-bit integer
• long int (or just long )
• always 32-bit integer
• signed versus unsigned integers
• you can put signed or unsigned keywords before
  the type
• we discussed signed integers
• signed is default
• unsigned integers use the same amount of bits but
  ranges are different
• 16-bit 0 ... 65,535 (216 1)
• 32-bit 0 ... 4,294,967,295 (232 1)

15
Numeric Types (contd)

• Real numbers in C
• Real literals
• 3.14159 -2.5 5.43e21
• Real data types (their difference is in
  precision)
• float
• consumes 4 bytes
• Range 0 U -1.175494351e38 ...
  -3.402823466e38
• U 1.175494351e38 ...
  3.402823466e38
• Tapestry does not like float
• double
• consumes 8 bytes
• Range 0 U -2.2250738585072014e308 ...
  -1.7976931348623158e308
• U 2.2250738585072014e308
  ... 1.7976931348623158e308
• Standard but a bit complex representation
• see floating point representation item in MSDN
  Library index

16
More on C types

• Check out these items in MSDN Library Index
• Fundamental types
• more on C types
• LIMITS.H header file
• limits of integer and char types
• floating limits
• limits for the floating points numbers (float,
  double)
• floating point representation
• if you are interested in to learn how the real
  numbers are represented in computers

17
Integer vs. Real

• Real values can be assigned to Integer variables,
  but this is not recommended since we loose
  precision
• int a
• double r
• r 125.879
• a r
• What is the value of a?
• 125
• Real value is truncated before storing in an
  integer variable
• Avoid doing this
• Compiler may not warn you
• Be careful when passing arguments to parameters
  as well
• passing an integer argument to a double parameter
  causes the same precision problem

18
Overflow

• Overflow occurs when the result of an integer
  expression is outside the limits
• See daysecs.cpp
• Run the program with
• 365 days
• result 31536000 seconds
• correct result and output
• 14500 days
• result 1252800000 seconds
• correct result and output
• 25129 days
• result -2123821696 seconds
• incorrect result and output due to overflow
• 65400 days
• result 1355592704 seconds
• incorrect result and output due to overflow

19
Arithmetic Operations

• Operators - /
• Operands values that operator combines
• variables or literals
• Syntax and semantics for arithmetic operations
• Addition, subtraction and ,
• for int, float and double
• 23 4 x y
  d 14.0 23
• Multiplication , for int, float and double
• 23 4 y 3.0 d 23.1 4
• Division /, different for int and real number
  types (double, float)
• for int operands result is the integer part of
  division
• 21 / 4 is 5 21 / 4.0 is 5.25 x / y
• Modulus , remainder of division, only for int
• 21 4 is 1 18 2 is 0 x y

20
Arithmetic Operations (contd)

• Mixed type expressions
• what if one operator is int but the other is
  double?
• integer is converted into double before operation
• 5.0 8 is 40.0
• 5 / 10 is 0 (integer division)
• 5.0 / 10 is 0.5 (real division)
• 10 8 is 2 (integer)
• 10 8.0 is 2.0 (double)

21
Expressions with several operators

• You can use parentheses in expressions
• Open and close parentheses should match
• Rule 1 Parenthesized subexpressions are
  evaluated first
• inside to out
• Rule 2 Within an expression/subexpression if
  there are several operators, use operator
  precedence,
• evaluate / before -
• Rule 3 If the operators are in the same
  expression/subexpression and at the same
  precedence level, then associativity rule applies
• evaluate operators from left to right
• Examples
• (5 - 3 (7-3)) 8 is -56
• 10 / 2 6 / 2 (5 - 3 (2 - 1)) is 17

22
Expressions with several operators

• Are the following expressions equivalent?
• (40 32) 5 / 9
• (40 32) (5 / 9)
• NO, first one is 4, second one is 0
• What about this?
• (40 32.0) 5 / 9
• Operations are double operations. Result is
  4.44444
• Are these operators sufficient?
• how to calculate square root?
• Later well study functions like sqrt, cos, sin,
  pow,
• For complicated mathematical operations that you
  cannot easily do using basic operators
• Accessible using include ltcmathgt (or ltmath.hgt)

23
Integer vs. Real (More on Precision)

• What is the difference between red and blue parts
  in the following program (fahrcels.cpp)?
• red integer arithmetic (low precision)
• blue real arithmetic (high precision)
• int main()
• int ifahr
• double dfahr
• cout ltlt "enter a Fahrenheit temperature "
• cin gtgt ifahr
• cout ltlt ifahr ltlt " F " ltlt (ifahr - 32)
  5/9
• ltlt " Celsius" ltlt endl
• cout ltlt "enter another temperature "
• cin gtgt dfahr
• cout ltlt dfahr ltlt " F " ltlt (dfahr - 32)
  5/9
• ltlt " Celsius" ltlt endl
• return 0

24
Reading Assignment

• Section 3.3
• Case Study Pizza Slices
• Similar to circle area calculation program
• Run the program pizza.cpp

25
More on Assignment operator (4.1 4.3.4)

• Assignment operator is
• to store values in variables
• variable expression
• first the right hand side expression is evaluated
  using the current values
• then the evaluated expression is stored in
  variable
• Types should be compatible, otherwise
• a syntax error may occur (e.g. string variable,
  integer expression), or
• precision is lost (e.g. integer variable, real
  expression)
• Example what is the value of a after the
  assignment?
• int a, b
• b 25 a 8
• a b 3 a 2
• Answer 3
• A rule If you use the left hand side variable in
  the right hind side expression as well, then the
  current value is used in the expression on the
  right hand side.

26
More on Assignment operator (4.1 4.3.4)

• Assigning single expression to several variables
• variable1 variable2 variable3 ... variablen
  expression
• all variables are assigned the same value of
  expression
• example
• int x, y, z
• x y z 5
• x, y and z contain 5
• Arithmetic assignment operators
• - /
• combines arithmetic operation and assignment in
  one operator
• variable expression is the same as
  variable variable expression
• example x 1 is the same as x x 1
• use analogy for - / and