Variables

1
Variables
2
Storing data

• Data is stored in our code by using variables and
  constants. We say that we assign a value to a
  variable or a constant.
• int total 3
• final price 100.25
• Assignment statements always assign from right to
  left, never left to right.

3
Data type

• Data types are used to separate data into whole
  numbers, real numbers, and character data.
• int and long refer to whole numbers. Use int for
  smaller whole numbers and long for really big
  numbers. We will look at this again when we get
  to number systems.
• float and double refer to real numbers ( numbers
  with a decimal point). The difference in these
  two is the precision of the number. Float is good
  to around 7 decimal places and double to
  around15.
• char is used for single characters. Strings are
  used for multiple characters. We will look at
  strings in more detail later.

4
Declaration statements

• int total3
• long amount123456789
• float myPay3.1512345
• double bigNumber1.123456789101112
• char firstInitialJ
• char lastInitialR

5
Naming variables

• While it is not a requirement for the program to
  run, it is important for clarity of reading and
  your grade in this class that you use descriptive
  names for your variables.
• int x 25 ?
• int totalSum 25 ?
• Notice that all words but the first are
  captitalized. Please do this in your work.

6
Note that the data types are drawn as different
sizes. This is because each data type is given a
predetermined size of memory (in bytes) by the
system depending on the data type. This is why we
have to declare out variables.
7

• Lets say an integer takes up four bytes of
  memory in our system.
• int total 0
• This declaration statement tells the system to
  reserve 4 bytes of memory to store this value and
  to give it an initial value of 0. The system has
  many memory locations referred to by some number
  like 0012FED4. Rather that having to remember
  this big hex number we are allowed to refer to
  the memory location by the identifier, in this
  case total. If we want to change the value of
  total to depend on the values of other variables
  we could write
• totalnumberOnHand-numberSold
• This assignment statement would change the value
  of total from 0 to whatever value
  numberOnHand-numberSold is equal to at this point
  in execution of the code. To change the value of
  total again we would have to write another
  assignment statement.
• We can use any math operation with little problem
  using variables as long as we pay attention to
  the data type and operator precedence.

8
Operator precedence

• Operator precedence basically means that any
  operators we use in our code have an order that
  they are read in when more than one of them
  appear on a single line. For our purposes.
• 1st parenthesis ( )
• 2nd multiply, divide, modulus , /,
• 3rd add ,subtract ,-
• The statement is read from left to right so for
  instance if we have and on the same line do
  the problem from right to left. If we have
  parenthesis on any line do this first. If we have
  for instance multiplication and addition on the
  same line do the multiplication first and then
  the addition.
• (48)/4 would be equal to 3.
• 48/4 would be equal to 6.
• 482 would be equal to 20.
• 482 would be equal to 34.

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10
Operator precedence
11
To display and input data

• cout
• cintotal
• cout
• cout and cin are keywords used for input/output
  in C programming. cout allows you to display to
  the screen and cin allows you to store keyboard
  input to a variable. The endl implies that any
  statement following will appear on the next
  line.

12
Compiler

• Any high level language has to be compiled or
  changed from the code we write to something the
  machine understands. In C the code is compiled
  to machine language. Machine language is 0s and
  1s or binary numbering.

13
Running the code

• When we run a console application we should see
  the DOS shell with whatever we told the system to
  write.