CMP 131 Introduction to Computer Programming

1
CMP 131Introduction to Computer Programming

• Violetta Cavalli-Sforza
• Week 5, Lecture 2 (Tuesday)

2
TODAY

• Input/Output and Formatting
• Your questions on everything before the Quiz
  tomorrow

3
Input/Output (Read/Write) Procedures

• Definitions
• Input Operation
• An instruction that reads data into memory.
• Output Operation
• An instruction that displays information stored
  in memory.
• Procedure
• A piece of code that is invoked from within the
  program and returns control to the program when
  finished
• I/O Procedure
• Pascal procedure that performs I/O operation.
• Procedure Call Statement
• An instruction that calls or activates a
  procedure.

4
Input/Output (Read/Write) Procedures

• Data can be stored in memory in three different
  ways
• Associated as a constant
• Assigned to a variable
• Read into a variable
• Reading is used if the data varies each time the
  program executes.
• Input/output procedures are supplied as part of
  Pascal compiler. Their names are standard
  identifiers.

5
The Same Identifier has Different Meanings in
Different Places

• When a variable name occurs in a read/readln and
  a write/writeln statement, it has a different
  meaning
• write(MyVar) MyVar is an expression The
  arguments to write are expressions (literals,
  constants, variables, combinations) whose value
  is retrieved for display
• read(MyVar) MyVar is interpreted as the address
  of a memory location to read into.You cannot
  have an expression as an argument to read
• Similarly, when a variable name occurs in an
  assignment statement, it has a different value on
  the right hand side (RHS) of the and on the
  left hand side of the
• On the RHS, it is (part of) an expression whose
  value is being retrieved
• On the LHS, it is the address of a memory
  location where the RHS value will be stored.

6
Reading Data

• Procedures read, readln
• Read data from standard input device input
  (e.g. keyboard)
• Syntax read/readln(inloc1, inloc2, ,
  inlocN)inlocX is a location where to store the
  data
• Examples
• read (SqMeters)
• readln (Letter1, Letter2, Letter3)
• read (Age, FirstInitial)
• Commas separate the variable names in input list

7
Reading Data

• Use write/writeln to display a prompt message
  when the user is required to enter data
• Otherwise the program is waiting and you dont
  know why or what to enter.
• The order of data enter must correspond to the
  order of variables in the input list
• Reading numeric data
• Insert one or more blanks between numeric data
  items
• Reading character or string data
• Don't insert any blanks between consecutive data
  items unless the blank character is one of the
  data items being read

8
Read vs. Readline Procedure

• Read
• Will read from input just as much as it needs for
  its arguments and leave the rest to be consumed
  later.
• Extra characters on the data line after a read
  operation are not read until the next read or
  readln operation
• Readln
• Will read from input just as much as it needs for
  its arguments
• It waits for a Return/Enter key character
• Extra characters on the data line between what is
  needed and the end of line will be ignored after
  ReadLn is finished

9

• PROGRAM ReadTest
• VAR x,y integer
• BEGIN
• write('Type 2 integers separated by a space gt
  ')
• read(x) writeln writeln('Read x ',x)
• read(y) writeln writeln('Read y ',y)
• writeln('Type ENTER to exit program.') readln
• END.

10

• PROGRAM ReadLnTest
• VAR x,y,z integer
• BEGIN
• writeln('Type 2 or more integers separated by a
  space.')
• writeln('Terminate your input by pressing
  ENTER.')
• readln(x,y)
• writeln('Read x ',x,' and y ',y)
• read(z)
• writeln('Read z ',z)
• END.

11
Writing/Displaying Data

• Procedures write, writeln
• Write data to standard output device output
  (e.g. terminal)
• Syntax write/writeln(expr1, expr2, ,
  exprN)where exprX is an expression, whose value
  is to be written, with optional formatting
  information
• Examples
• writeln (Letter1, Letter2, Letter3)
• write (Age , Age, First Initial
  ,FirstInitial)
• write (SqMeters102)
• Commas separate the variable names in output list
• Writes every argument in the output list in the
  order in which it is given.

12
write vs. writeln Procedure

• writeln
• used to display a line of program output,
  including a newline at the end cursor advances
  to the next line after the output is displayed.
• without any output list instructs the output
  device to advance by a blank line
• write
• Cursor doesn't advance to the next line after the
  output is displayed.

13
Self-Check

• What is the output if the entered data are 5 7?
• writeln (Enter two integersgt)
• readln(M, N)
• M M 5
• N 3 N
• writeln (M , M)
• writeln (N , N)
• What of the output of this code?
• write (My name is)
• writeln (Doe, Jane)
• writeln
• write(I live in )
• write(Ann Arbor, MI)
• writeln (and my zip code is , 48109)

14
No Formatting with write/writeln

• Integer values take the space they need
• Real values Most Pascal compilers use scientific
  notation (floating-point notation) to display
  real values, but you can change that with
  formatting directives.
• Character values display as themselves, without
  quotes
• Boolean values display as FALSE and TRUE with no
  quotes
• String literals, the characters inside the quotes
  are printed, but not the quotes themselves

15

• PROGRAM TestOutputNoFormat
• BEGIN
• writeln('An integer with no formatting ',
  45)
• writeln('A real with no formatting ', 45.67)
• writeln('A character with no formatting ',
  '')
• writeln('Boolean values, no formatting ',
  false, ' and ', true)
• END.

16
Formatting Integer Output

• Formatting Integer Values b stands for blank
  space
• Value Format Printed Output
• 234 4 b234
• 5 bb234
• 1 234
• Len bb234 (if Len5)
• -234 4 -234
• 5 b-234
• 1 -234

17
Formatting Integer Output

• Add the symbol n to the integer output list
  item, where n specifies the number of digits to
  be displayed (field width).
• The digits will be right-justified.
• For negative numbers, the minus sign is included
  in the counts of digits displayed
• The format specification 1 can always be used
  to display any integer values without leading
  blanks.
• The field width specification may be a variable,
  or even an expression
• The syntax for each integer item in an output
  list is ltinteger expressiongtltinteger
  expressiongt

18

• PROGRAM TestOutputIntFormat
• VAR Dollars, Cents integer
• BEGIN
• Dollars 5 Cents 33
• writeln('Your collection was worth ')
• writeln(Dollars 1, ' dollars', ' and ', Cents
  1, ' cents. ')
• writeln(Dollars 2, ' dollars', ' and ', Cents
  2, ' cents. ')
• writeln(Dollars 3, ' dollars', ' and ', Cents
  3, ' cents. ')
• writeln(Dollars 4, ' dollars', ' and ', Cents
  4, ' cents. ')
• writeln(Dollars 5, ' dollars', ' and ', Cents
  5, ' cents. ')
• Dollars -2 Cents 89
• writeln('but is now worth ')
• writeln(Dollars 1, ' dollars', ' and ', Cents
  1, ' cents. ')
• writeln(Dollars 2, ' dollars', ' and ', Cents
  2, ' cents. ')
• writeln(Dollars 3, ' dollars', ' and ', Cents
  3, ' cents. ')
• writeln(Dollars 4, ' dollars', ' and ', Cents
  4, ' cents. ')
• writeln(Dollars 5, ' dollars', ' and ', Cents
  5, ' cents. ')
• END.

19
Formatting Real Output

• Examples b stands for blank space
• Value Format Printed Output
• 3.14159 52 b3.14
• 42 3.14
• 32 3.14
• 51 bb3.1
• 85 b3.14159
• 9 3.142E00
• -3.14159 9 -3.14E00
• -124.3163 42 -124.32

20
Formatting Real Output

• Total field width desired number of decimal
  places should be indicated.
• Add nd to the integer.
• n total field width
• d number of decimal digits.
• Total field width should be large enough to
  accommodate all digits before and after the
  decimal point
• Pascal will use the extra space it needs anyhow
  so your nicely formatted data may not look so
  well formatted after all.
• Decimal point sign for negative numbers are
  included in the count.
• It is possible to use the form n for real
  numbers. In this case, the real value is printed
  in scientific notation using a total of n print
  positions.

21
Formatting Real Output

• Eliminating Leading Blanks
• Choose a format that will display the smallest
  value expected without leading blanks..
• Examples
• 29397 1 is displayed as 29397
• 99397.567 31 is displayed as 99397.6
• To display a real value without leading blanks,
  use format specification 31 for one decimal
  place or 42 for two decimal places.
• If you use n, the scientific notation will be
  displayed.

22
Formatting Character String Output

• Formatting Strings
• A string value is always printed right-justified
  in its field.
• If the field width is too small to accommodate
  the string value, Pascal will take the space it
  needs.
• Examples b stands for blank space
• String Format Printed Value
• '' 1
• 2 b
• 'ACES' 1 ACES
• 2 ACES
• 3 ACES
• 4 ACES
• 5 bACES

23

• PROGRAM TestOutputStringFormat
• BEGIN
• writeln('ACES'1)
• writeln('ACES'2)
• writeln('ACES'3)
• writeln('ACES'4)
• writeln('ACES'5)
• writeln('ACES'6)
• END.

24
Self-Check

• Show how the value -15.564 (stored in X) would be
  displayed using the following formats
• X 84 X83 X81 X80 X8
• Assuming X 12.345 (type Real) and I 100 (type
  Integer). What will the output of the following
  statements look like?
• writeln(X is 10, X 62, I is 4, I 5)
• write(I is 10, I 1)
• writeln(X is 10, X 21)