Basic Expressions and String Manipulation

1
Basic Expressions and String Manipulation

• Week 4
• Department of Computer Science
• Faculty of Science and Technology
• Assumption University

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Agenda

• Basic C Operators
• Assignment Operators
• Arithmetic Operators
• Relational and Equality Operators
• Logical Operators
• Mixed Type Expressions
• Order of Precedence
• Advanced C Operators
• Strings and String Manipulation

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Assignment Operator

• The assignment operator assigns a value to a
  variable.
• a 5
• a b
• a 2 (b 5)
• a b c 5

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Arithmetic Operators

• The five arithmetical operations supported by the
  C language are
• OPERATOR MEANING
• Addition
• - Subtraction
• Multiplication
• / Division
• Modulo

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Arithmetic Expression

• int i1,i2,i3
• float f1,f2,f3
• double d1,d2,d3
• i1 1 f1 1.05 d1 1.05
• i2 2 f2 2.985 d2 2.985
• i3 i1 i2 f3 f1 f2 d3 d1 d2
• i3 i1 - i2 f3 f1 - f2 d3 d1 - d2
• i3 i1 i2 f3 f1 f2 d3 d1 d2
• i3 i1 / i2 f3 f1 / f2 d3 d1 / d2
• i3 i1 i2

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Mixed Type Expression

• int n
• double x
• x n // is of type double
• n 4 // is of type int
• n 4.0 // is of type double

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Precedence of Operators

• When writing complex expressions with several
  operands, which operand is evaluated first and
  which later.
• a 5 7 2
• We may doubt if it really means
• a 5 (7 2) // with a result of 6, or
• a (5 7) 2 // with a result of 0
• Multiplication (), Division (/), and Modulo ()
  have precedence over Addition () and Subtraction
  (-).

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Relational and Equality Operators

• The result of a relational operation is a Boolean
  value that can only be true or false, according
  to its Boolean result.
• OPERATOR DESCRIPTION
• Equal to
• ! Not equal to
• gt Greater than
• lt Less than
• gt Greater than or equal to
• lt Less than or equal to

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Relational and Equality Operators
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Logical Operators

• The operator ! is the C operator to perform the
  Boolean operation NOT.
• The operator corresponds with Boolean
  operation AND.
• The operator corresponds with Boolean
  operation OR.
• OPERATOR DESCRIPTION
• ! NOT
• AND
• OR

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Logical Operators

• !(55) // evaluates to false because (5
  5) is true.
• !(6lt4) // evaluates to true because (6 lt
  4) is false.
• !true // evaluates to false
• !false // evaluates to true.
• ((55) (3gt6)) // evaluates to false (true
  false).
• ((55) (3gt6)) // evaluates to true ( true
  false ).

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Agenda

• Basic C Operators
• Advanced C Operators
• Compound Operators
• Increase and Decrease
• Conditional Operator
• Comma Operator
• Explicit Type Casting Operator
• Strings and String Manipulation

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Compound Assignment

• We can use compound assignment operators to
  modify the value of a variable
• a b ? a a b
• a - b ? a a - b
• a b ? a a b
• a / b ? a a / b
• a b ? a a b

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Compound Assignment

• include ltiostreamgt
• using namespace std
• int main ()
• int a, b 3
• a b
• a 2 // equivalent to a a 2
• cout ltlt a
• return 0

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Increase and Decrease

• The increase operator () and the decrease
  operator (--) increase or reduce by one the value
  stored in a variable.
• They are equivalent to 1 and to -1,
  respectively. c
• c1
• cc1

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Conditional Operator

• The conditional operator evaluates an expression
  returning a value if that expression is true and
  a different one if the expression is evaluated as
  false. Its format is
• condition ? result1 result2
• If condition is true the expression will return
  result1, if it is not it will return result2.

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Conditional Operator
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Explicit Type Casting Operator

• Type casting operators allow you to convert a
  datum of a given type to another.
• There are several ways to do this in C.
• int i
• float f 3.14
• i (int) f
• i int (f)

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Agenda

• Basic C Operators
• Advanced C Operators
• Strings and String Manipulation
• String
• String Input
• String Concatenation
• Built-in String Functions

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Strings

• String objects are a special type of container,
  specifically designed to operate with sequences
  of characters.
• Unlike traditional c-strings, which are mere
  sequences of characters in a memory array, C
  string objects belong to a class with many
  built-in features to operate with strings in a
  more intuitive way and with some additional
  useful features common to C containers.

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Strings

• Before you can use this type, you must bring in
  the string definition with the statement
  include ltstringgt
• After this you can declare strings like any other
  variable. For example string variable
• A string constant is any text enclosed in double
  quotes. For example my_name "Steve"

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Strings

• include ltiostreamgt
• include ltstringgt
• using namespace std
• int main ()
• string str1, str2, str3
• str1 "Test string " // c-string
• str2 'x' // single character
• str3 str1 str2 // string
• cout ltlt str3 ltlt endl
• return 0

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String Input

• include ltiostreamgt
• include ltstringgt
• using namespace std
• int main ()
• string line
• cout ltlt "Please introduce a text.\n"
• getline(cin,line)
• cout ltlt "The text you introduced was\n" ltlt
  line
• return 0

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String Concatenation

• include ltiostreamgt
• include ltstringgt
• using namespace std
• int main( )
• string first_name // Declare first string
• string last_name // Declare second string
• string full_name // Declare third string
• first_name "Oliver"
• last_name "John"
• // concatenate strings using
• full_name first_name " " last_name
• cout ltlt "Full name is " ltlt full_name ltlt '\n'
• system("PAUSE")
• return 0

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String Functions

• string.size() Return length of string
• string.length() Return length of string
• string.capacity() Return size of allocated
  storage
• string.max_size() Return maximum size of string
• string.at() Get character in string
• string.substr() Generate substring
• string.find() Find content in string

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String Functions

• include ltiostreamgt
• include ltstringgt
• using namespace std
• int main ()
• string str ("Test string")
• cout ltlt "size " ltlt str.size() ltlt "\n"
• cout ltlt "length " ltlt str.length() ltlt "\n"
• cout ltlt "capacity " ltlt str.capacity() ltlt "\n"
• cout ltlt "max_size " ltlt str.max_size() ltlt "\n"
• cout ltlt char at 4 " ltlt str.at(4) ltlt "\n"
• return 0

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String Extraction

• include ltiostreamgt
• include ltstringgt
• using namespace std
• int main ()
• string str"We think in generalities, but we
  live in details."
• string str2, str3
• str2 str.substr(12,12) // "generalities"
• pos str.find("live") // position of
  "live" in str
• str3 str.substr(pos) // get from "live"
  to the end
• cout ltlt str2 ltlt ' ' ltlt str3 ltlt endl
• return 0