Chapter 3' Expressions and Interactivity

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Chapter 3. Expressions and Interactivity
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PROGRAM INPUT
Input Stream and the Extraction Operator
gtgt include ltiostreamgt General Format cin gtgt
variable gtgt variable int cost //declare int
data type cin gtgt cost // get data and store in
cost The C system matches the variable with
the correct data type in the input buffer, if
possible.
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THE READING MARKER

• The Reading Marker indicates the next data item
  to be read.
• The extraction operator leaves the reading marker
  positioned after the last data item read.
• The NEWLINE character is created when the RETURN
  or ENTER key is depressed.
• The endl manipulator also outputs a newline.
• The newline may be created in code this way
  \n
• tick backslash n tick
• You can store the newline character in a
  character data item.

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Entering Multiple Values

• The cin object may be used to gather multiple
  values at once.

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Reading Strings

• cin can read strings as well as numbers.
• Strings are stored in character arrays.
• char Name10
• Name has 9 bytes for data, 1 byte for the Null
  delimiter

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MATHEMATICAL EXPRESSIONS
rvalue expression is assigned lvalue
expression // ONE equal sign is the assignment
operator sum 12 4 sum 10
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PRECEDENCE AND ASSOCIATIVITY

• PRECEDENCE defines the priority with which each
  operator in an expression will be applied.
• ASSOICATIVITY defines the order of evaluation of
  operators in an expression, containing operators
  of the same precedence. If the evaluation is
  from left to right, the operator is termed
  left-to-right associative. Otherwise, the
  operator is right-to-left associative.
• EXAMPLE
• 4 - 2 is evaluated (5 4) - 2
• a b c is evaluated (a b ) c
• X y 2 is evaluated X ( y 2 )

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Type Coercion or Widening or Promotion long
double double float unsigned long long unsigned
int int char
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EXPLICIT COERCION or WIDENING or PROMOTION The
programmer can explicitly change the data type
for the instance of the computation or
assignment. Float(someint) somefloat 4.8
float(someInt 3) // result is a float Example
int sum 60 int count 80 float average
0.0 / Wrong / average sum/count //
result is 0.0 / Right!!! / average
static_castltfloatgtsum / static_castltfloatgtcount
average (float)sum/(float)count / either
result will be 0.75 /
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The define Preprocessor Directive

• define PI 3.14159 // no semicolon, please!
• is roughly the same as
• const float PI3.14159 // always a float!
• PI is always a float in the second statement.

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Formatting Output With Member Functions

• cout.width(11) //calls the width member
  function,
• //same as setw(11)
• cout.precision(2) //sets precision to 2
  significant digits
• cout.setf(iosfixed) //same as
  setiosflags(iosfixed)
• --OR--
• //To display fixed point, decimal point and
  left-justify
• cout ltlt setprecision(2) ltlt fixed ltlt showpoint ltlt
  endl
• // To disable flags
• cout ltlt right

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• FORMATTING INPUT
• Three ways to format input
• char Name10
• cin.get(Name,10)
• char Name10
• cin gtgt setw(10) gtgt Name
• char Name10
• cin.width(10)
• cin gtgt Name

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Char String5 100 101 102 103
104 cin.width(5) cin gtgt String Morris\n
Reading Marker There is now
garbage in the input buffer.
100 101 102 103 104 M o r r \0
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Reading a Line of Input

• cin.getline(Name, 15)
• Only 14 characters will be read.