Variables and C Data Types

1
Variables and C Data Types
2
Variables

• Programs like Hello World seen in the last
  lecture has little use in practice
• There is no room for change. It simply prints a
  predetermined string onto the screen every time
  it is executed.
• A more interesting program might have different
  behavior under different circumstances.

3
Variables (cont)

• For instance, a program that asks for two numbers
  and outputs their sum is much more useful than
  the previous.
• This program needs placeholders for the incoming
  values.
• These placeholders are called variables

4
Variables (cont)

• Variables are used to hold data within a program
  (the data is held in your computers main
  memory).
• A program can read-from and write-to variables.
  That is, their values can vary.
• Every variable consists of two parts
• The name of a variable is tied to a location in
  memory.
• Its data type.

5
Data Type Integers

• An integer value is any number that has no
  decimal point.
• 123 -45000 1432431 0
• are all valid integers.
• 1,244 is not a valid integer in C no commas
  are used. Neither is 12 because is not a valid
  part of an integer.

6
Data Type Integers (cont)

• The largest and smallest integers supported is
  dependent of the computer on which the program is
  compiled.
• Most of todays computers use 32-bits to
  represent an integer, so 232 values can be
  represented.
• Integers can be signed or unsigned.
• Unsigned integers only account for 0 and positive
  numbers.
• Signed integers need also account for negative
  numbers.
• So if 232 numbers can be represented in 32-bit
  systems, will the sign factor affect the range of
  supported integers???
• Yes Indeed it will.
• Unsigned Integers will range from 0 to
  4294967295.
• Signed Integers will range from -2147483648 to
  2147483647.

7
Data Types Floating Point Numbers

• Floating-point numbers have a decimal point, and
  they can also be signed or unsigned.
• There are three types float, double, or long
  double.
• The differences between these are their supported
  range and precision.

8
Data Types Floating Point Numbers (cont)

• To represent a floating point number
• float uses 32 bits (4 bytes)
• double uses 64 bits (8 bytes)
• long double uses 128 bits (16 bytes)
• The tradeoff is storage vs. precision and range.
• What exactly is the precision and range, and how
  are floating point numbers represented in binary
  format?

9
Data Types Floating Point Numbers (cont)

• Floating-point numbers can be written in
  exponential notation
• 134.56 or 1.3456e2
• -0.00345 or -3.45e-3
• Here, e is short for times ten to the power of,
  just like in scientific notation.
• float Range /- 3.4e /- 38 (7 digits)
• double Range /- 1.7e /- 308 (15 digits)
• long double Range /- 1.7e /- 308 (15 digits)
  

10
Data Type Characters

• Characters include
• All letters of the alphabet (upper and lower
  case).
• The symbolic representation of digits 0 9.
• All various symbols such as , !
• A character value is simply one of these in
  single quotes, such as A or 8.
• Note here, though, 8 is NOT the same as 8
  because 8 is the symbolic representation of the
  character, 8, and 8 is the integer 8

11
Data Type Characters (cont)

• Characters usually take up 8 bits (1 byte)
• That means there are 28 (or 256) different
  characters, and every number within the range of
  0, 255 is mapped onto some character.
• So a character really boils down to a numerical
  representation known as ASCII encoding.
• See http//www.asciitable.com for a list of all
  256 characters and their corresponding codes.

12
Data Type Boolean

• The Boolean data type is used for just two
  values true and false
• Like characters, they only consume 1 byte of
  storage.
• It is worth noting that when dealing with Boolean
  values in C, any number other than 0 is always
  interpreted as true.

13
Arithmetic Operations

• The basic operations of , - , , and / are
  available, as is which is used for modulus
  division (returns the remainder).
• A simple arithmetic expression is of the form
• operand operator operand
• 5 3
• So.. how can you use them in a program?

14
Arithmetic Operations (cont)

• // Performs some arithmetic operations
• include ltiostream.hgt
• using namespace std
• int main()
• cout ltlt 5 3 ltlt (5 3)
• cout ltlt \n 4 3 ltlt (4 3)
• cout ltlt \n 5 / 2 ltlt (5 / 2)
• return 0

15
Integer Division

• In C, (15 / 2) is 7.
• Remember that integers have no fractional parts
• There is no rounding in integer division. If your
  program contained
• cout ltlt (15 / 16)
• The output would be 0.
• The fractional part of an integer division is
  truncated so the result can be an integer.
• If you need the remainder, use .
• If you need a decimal answer, make your operands
  floating-point numbers
• cout ltlt (15.0 / 16.0)

16
Expression Types

• An expression that contains only integer operands
  is an integer expression.
• An expression that contains only floating point
  operands is a floating-point expression.

17
Mixing Expression Types

• A mixed-mode expression has both floating-point
  and integer data types.
• The rules governing the data type of the result
  are
• If both operands are integers, the result is an
  integer.
• If one operand is a floating-point number, then
  the result is a double.

18
Operator Precedence andAssociativity

• The minus sign can also be used as a unary
  operator that serves to negate the sign of a
  number.

19
Declaration Statements

• Before you can use a variable, you must declare
  it.
• This allows the computer to set aside the memory
  that will be needed for that variable.
• Recalling that variables consist of a name and
  its data type, C variable declarations are of
  the form
• dataType variableName
• dataType can be int, float, char, double, long
  double, unsigned int, ...
• variableName must obey the identifier rules we
  discussed.

20
Declaration Example

• include ltiostream.hgt
• using namespace std
• int main()
• int age
• float wage
• char initial
• long double height
• return 0

21
Variable Assignments

• Variables can be assigned values during or after
  declaration, but never before (why?)
• Assignment is done with the equals sign
• height 67.34
• initial E
• //initial E will not work as expected.
• double totalPay salary overtime
• Variable assignment is NOT commutative! The
  variable must always be on the left side of an
  equals sign. The following is NOT valid
• 67 x

22
Assignment Example

• include ltiostream.hgt
• using namespace std
• int main()
• double totalPaid
• double numberPaid
• double averagePaid
• char initial
• totalPaid 58.24
• numberPaid 14.0
• averagePaid (totalPaid / numberPaid)
• initial D
• cout ltlt My first initial is ltlt initial ltlt
  \n
• initial C //Assigned a new value.
• cout ltlt My last initial is ltlt initial ltlt
  \n
• cout ltlt The average I paid is ltlt averagePaid
  ltlt \n
• return 0

23
Multiple Declarations

• In the previous example we had
• double totalPaid
• double numberPaid
• double averagePaid
• This can be done in one statement like this
• double totalPaid, numberPaid, averagePaid
• This is very useful when creating several
  variables of the same type.

24
Initialization

• Variables can be assigned a value as they are
  declared. This is called initializing.
• include ltiostream.hgt
• using namespace std
• int main()
• double totalPaid 58.24
• double numberPaid 14.0
• double averagePaid (totalPaid / numberPaid)
• char initial D
• cout ltlt My first initial is ltlt initial ltlt
  \n
• initial C
• cout ltlt My last initial is ltlt initial ltlt
  \n
• cout ltlt The average I paid is ltlt averagePaid
  ltlt \n
• return 0