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Escape Sequence Characters

• \n new line
• \r carriage return
• \t horizontal tab
• \v vertical tab
• \b backspace
• \\ backslash
• \ double quotation mark
• \ single quotation mark
• \? Question mark
• \ddd ASCII code in octal format
• \xdd ASCII code in hexadecimal format

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Flow Control 1Decision Statements

• Boolean Expressions
• Evaluate to TRUE (1) or FALSE (0) only. C uses
  integer to represent Boolean variables, 0 for
  FALSE and 1 for TRUE. However, any non-zero
  integer is regarded TRUE in C.
• Relational Operations
• Comparison between numerical quantities
• Evaluate to TRUE (1) if relation is satisfied and
  FALSE (0) otherwise.
• gt (greater than), gt (greater than or equal to)
• lt (less than), lt (less or equal to)
• (equal to), ! (not equal to)

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Decision Statements

• Boolean (Logic) Expressions
• Operations on Boolean Variables
• Binary (AND), (OR)
• Unary ! (NOT or INVERSION)
• Truth Table in C
• Strictly speaking, Boolean algebra has only TRUE
  (1) or FALSE (0) but no non-zero.

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Decision Statements

• The AND () operator evaluates to true only when
  both operands are TRUE. If the first operand is
  FALSE, we dont need to know the second operand
  for evaluation. Similarly, the OR () operator
  evaluates to FALSE only when both operands are
  FALSE. If the first operand is TRUE, we dont
  need to know the second one. This is called
  short-circuit evaluation.

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Arithmetic Expressions

• Assignment operator
• The equal sign assigns the value of the
  variable on its right to the memory location of
  the variable on its left. Unlike in mathematics
  where x x 1 is meaningless, in C, the same
  expression means take the present value stored in
  the memory location corresponding to the
  identifier x, add 1 to it and store the result
  back to the same memory location. (x x 1 is
  usually written as x 1 in C).
• Arithmetic Operators
• - / (modulus, i.e. positive remainder of
  integer division)
• Relational operators (return 1 if true and 0 if
  false)
• (equal to) ! (unequal) lt
  gt lt gt (and) (or)
  ? (conditional operator)
• Assignment Operators
• - / gtgt
  ltlt
• Shift Operators ltlt gtgt
• Bitwise Operators
• Others ! ( ) --gt , .

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• Operator Precedence
• An expression may contain multiple operators,
  operator precedence defines the order that
  operators in an expression are evaluated when
  multiple operators are present. The operator
  precedence in C is largely the same as the
  convention used in arithmetic, i.e.
• 1. Function calls in an expression
• 2. Multiplication () and division (/) are
  performed in sequence
• 3. Addition () and subtraction (-).
• Operator precedence can be overwritten by using
  parentheses. It does no harm to put parentheses
  to force the sequence of the operation you want
  to perform when you are uncertain of the operator
  precedence.

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• Precedence and associativity of operators
• C allows concantenation of operators.
  Precedence rule defines the order of operators
  and associativity defines the sequence of
  operation (from left to right or from right to
  left).
• Examples
• 1. is right associative, ? a b 5
  ? a (b 5)
• 2. and / , are left associative, ? a b
  / c ? (a b) / c
• 3. int a 4, b 5
• double c, d
• c a / b 2.0 / c 0.0 /
• d 2.0 a / b / d 1.6 /
• 4. lt and gt have higher precedence than ,
• ? a gt b a lt c ? (a gt b)
  (a lt c)
• 5. has higher precedence than gt, ? a b gt
  0 ? (a b) gt 0

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• Type of expression and conversion
• The data type of the result of an expression such
  as xy is the same as x and y if x and y are the
  same type
• If x is int and y is double or vice versa, then
  the int is converted to double first before
  operation, the result is double
• General rule for mixed-type expressions the
  smaller operand is promoted (converted) to the
  biggest-range data type (normally double) before
  evaluation, e.g. x is int and y is char, then y
  is promoted to int first and xy evaluates to an
  int result.
• If an assignment operator is used to assign the
  result of an expression to another variable, the
  expression is evaluated first according to the
  above conversion rule and the result is assigned
  to the value. Another conversion occurs if
  necessary.

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Example

• int x, y
• double u, v
• x y u / yu is evaluated as double
  first. /
• / result is converted to int before
  assigned to x. /
• v x y / xy evaluated as int first. /
• / result is converted to double before
  assigned to v. /
• Conversion from double to int may result in loss
  of precision, e.g. if y u 2.4, x will be
  evaluated to 2.
• We can overwrite default conversion rule by
  casting, e.g. x and y can be cast as double
  before evaluation.
• V (double)x (double)y
• x 3
• y 5
• u x/y / u 0.0, this is a common mistake
  /
• v (double)x / (double)y / v 0.6 /

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Type Casting

• Syntax
• (data_type) Identifier
• data_type(Identifier)
• static_castltdata_typegt(Identifier)

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• if statement
• Syntax if (condition)
• statement
• The statement following the condition is executed
  only when the condition is satisfied, e.g.
• if (i 0)
• cout ltlt i is zero

• if-else statement
• Syntax if (condition)
• statement1
• else
• statement2

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• If condition is satisfied, execute statement1,
  otherwise execute statement2.
• Example
• if (a gt b)
• cout ltlt a is bigger than b.\n
• else
• cout ltlt a is not bigger than b.\n
• We can use Boolean operators to set compound
  conditions, e.g. validating the range of
  certain input a
• if (a lt 0 a gt 5)
• cout ltlt a is out of range.\n
• else
• cout ltlt You have entered ltlt a ltlt endl

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• Compound statement
• Sometimes a simple statement after the if test
  condition is not enough to accomplish our job.
  We can use compound statement to achieve more
  complicated tasks.
• A compound statement is a sequence of statements
  enclosed in open and closed braces, e.g.
• if (a gt b)
• c a - b
• cout ltlt a is bigger than b by ltlt c ltlt
  endl
• else
• cout ltlt a is smaller than or equal to
  b.\n
• A compound statement defines a new level of
  variable scope. You can declare local variables
  for the compound statement within the braces.

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• Local variables in the compound statement are
  only visible by the compound statement. However,
  local variables in the same function are also
  visible to the compound statement. Example
• int x, y
• if (T gt 37.0)
• double fah
• fah T1.8 32
• cout ltlt Patient is on fever. The
  equivalent body temperature in
• Farenheit is ltlt fah ltlt endl
  
• else
• cout ltlt Body temperature is fine.\n
• discharge()

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• x and y are visible by the whole function. fah
  is only visible to the compound statement in
  which it is declared. Memory space for fah is
  allocated when the compound statement is reached
  and returned to the OS when the compound
  statement is finished.
• Use indentation for compound statements to
  enhance readability. Indentation is for human
  readers only. The compiler only recognizes the
  braces, not the indentation.
• The indentation format used in the examples is
  the ATT Bell Labs programming style.

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• Alternative to compound statement
• Use a comma separated list of expressions.
• The comma operator basically does nothing.
  Expressions separated by comma evaluates from
  left to right.
• Not as clear and readable as compound statement.
• Example
• if (a gt b)
• c a - b, a 2
• Empty statement
• A single semicolon . No operation. Mostly
  used in for loops. Example
• if (a gt b)

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• More on C syntax and common mistakes
• Since C treats Boolean variables as integers
  and allows mixing of operators, it is easy to
  make some mistakes.
• Do not confuse (equality) with
  (assignment)
• if (a 5) statement is interpreted as
• (1) a 5 evaluates to 1 if condition is
  satisfied, 0 otherwise.
• (2) if (1 / non-zero /), statement is
  executed.
• if (a 5) statement is interpreted as
• (1) 5 is assigned to variable a first
• (2) if (5 / non-zero /), statement is executed
  (ALWAYS)
• if (a ! 0) can be written as if (a)

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• if (0 lt x lt 4) is syntactically correct but
  not always logically correct. Use associativity
  and precedence rules, the sequence of operations
  in the parenthesis is
• (0 lt x) lt 4, when x gt 4, the final result
  must be 1 (TRUE).
• Correct expression if (0 lt x x gt 4)
• The ! (NOT) operator has higher precedent than
  relational operators, so ! 4 gt 5 is interpreted
  as (!4) gt 5 which is 0 instead of ! (4 gt 5)
  which is 1.
• To represent both x and y are greater than z,
  write
• (x gt z) (y gt z), NOT x y gt z which
  is actually
• x (y gt z)
• Although the parentheses in (x gt z) (y gt z)
  are not required, the expression is more
  readable if the parentheses are included.

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• Logical assignments
• The expression following the assignment operator
  represents logic ideas. As we said, the logic
  variable is nothing but an integer variable or
  bool variable.
• Examples
• even n2 0
• is_letter (A lt ch ch lt Z)
  (a lt ch ch lt z)
• in_range n gt -10 n lt 10

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• Nested if and multiple alternative decisions
• Sometimes, we need to make more than two
  decisions.
• Syntax if (condition1)
• statement1
• else if (condition2)
• statement2
• else if (conditionN)
• statementN
• else
• default_statement
• One and only one statement will be executed.
• The last else and the default statement are
  optional.

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• Example Increment the counters num_pos,
  num_new or num_zero depending on the sign of the
  input value x.
• Implementation 1
• if (x gt 0)
• num_pos 1
• else if (x lt 0)
• num_neg 1
• else / x 0 /
• num_zero 1
• Implementation 2
• if (x gt 0)
• num_pos 1
• if ( x lt 0)
• num_neg 1
• if (x 0)
• num_zero 1

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• Both implementations give the same result.
• Implementation 1 is clearer and more efficient.
• The three if conditions in implementation 2 are
  examined for every x. However, if x is positive,
  the other two else conditions are not examined.
  So the program runs faster.
• Use indentation properly to enhance readability.
• In nested if-else structure, the else statement
  always matches the last incomplete if statement
  regardless of indentation.
• Order of conditions can be important in certain
  situations.

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• Example
• if (income lt 15000)
• cout ltlt Lower class.\n
• else if (income lt 55000)
• cout ltlt Middle class.\n
• else / income gt 55000 /
• cout ltlt Upper class.\n

A guy with annual income 10000 will be
classified as lower class by the above code. If
we reorder the conditions if (income lt
55000) cout ltlt Middle class.\n else if
(income lt 15000) cout ltlt Lower
class.\n else cout ltlt Upper class.\n
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• The second if is never used in the reordered
  code. The condition income lt 15000 is included
  in the condition income lt 55000. Only mutually
  exclusive conditions can be placed in arbitrary
  order.
• Example Use compound statement to overwrite the
  default if-else paring. Consider the following
  code
• a 4
• b 4
• if (a 4)
• if (b 4)
• cout ltlt Both a and b are 4.\n
• else
• cout ltlt a is not 4.\n

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• In spite of the indentation, the else statement
  is associated with the second if. Therefore
• a 4 and b 2 ? output a is not 4
• a 2 and b 2 ? output no text
• Correction 1
• if (a 4)
• if (b 4)
• cout ltlt Both a and b are 4.\n
• else
• cout ltlt a is not 4.\n

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• Correction 2
• if (a 4 b 4)
• cout ltlt Both a and b are 4.\n
• else if (a ! 4)
• cout ltlt a is not 4.\n
• Multiple decisions using the switch statement
• Useful when the selection is based on the value
  of a single variable or of a simple expression
  called the control expression
• Syntax switch (expression) / usually a
  variable /
• case label1
• statement1
• statement2
• break

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• case label2
• statement1
• statement2
• break
• case labelN
• statement1
• statement2
• break
• default
• statement1
• statement2
• break / optional here /

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• When a match between the value of the control
  expression and the case label is found, the
  statements following the case label are executed
  until a break statement is found. The break
  keyword skips the rest of the switch options.
• Omission of the break keyword before the next
  case label will cause the execution of the
  statements following the next case label. This
  is called execution fall through. It is a useful
  feature in C programming.
• Example
• In this example, the user types in a character
  input. Different functions are called according
  to the input character. Functions e_mail(),
  news(), quit(), re_input() are defined somewhere
  in the program.

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• Switch (input)
• case e
• case E
• email()
• break
• case n
• case N
• news()
• break
• case q
• case Q
• quit()
• break
• default
• re_input()

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• Limitations labels can only be integers or
  characters (i.e. something that can be evaluated
  to an integer).
• The statements in the default sections are
  executed when there is no match with all the
  labels. Although the default section is
  optional, it is recommended that a default
  section is always included whenever possible.
• Remember to put the break statement at the end of
  each alternative to prevent fall through.
• Conditional Operator ?
• Ternary operator with syntax
• expression1 ? expression2 expression3

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• Evaluates expression1 first. If it is non-zero
  (true), expression2 is evaluated and the result
  of expression2 is the value of the conditional
  expression as a whole.
• If expression1 evaluates to zero (false),
  expression3 is evaluated. The result of
  expression3 is then the value of the whole
  conditional expression.
• Example
• if (y lt z)
• x y
• else
• x z
• can be equivalently written as
• x (y lt z) ? y z

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Homework

• Homework 1
• Page 105, 1
• Page 106, 6
• Finish reading chapters 1 and 2