Expressions and Statements

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Expressions and Statements

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Statements

• Statements end with the semicolon

x a b / this adds the values of a and b
and assigns the result to x / / this is
the null statement, it does nothing /
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Whitespace

• White spaces are tabs, spaces, and newlines
• White spaces are generally ignored
• These are all equivalent,
• but some are easier to read than others.

xab x a b x a b
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Whitespace sometimes matters

• These are not equivalent
• Use common sense

OurWeight MyWeight YourWeight Our Weight
My Weight Your Weight
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Blocks and Compound Statements

• Blocks begin with the left brace and end with
  the right brace
• Blocks are not terminated with a semicolon

temp a a b b temp
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Blocks and Compound Statements

• Blocks begin with the left brace and end with
  the right brace
• Blocks are not terminated with a semicolon

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Blocks and Compound Statements

• Blocks begin with the left brace and end with
  the right brace
• Blocks are not terminated with a semicolon

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Blocks and Compound Statements

• Blocks begin with the left brace and end with
  the right brace
• Blocks are not terminated with a semicolon

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Blocks and Compound Statements

• Blocks begin with the left brace and end with
  the right brace
• Blocks are not terminated with a semicolon

temp a
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Blocks and Compound Statements

• Blocks begin with the left brace and end with
  the right brace
• Blocks are not terminated with a semicolon

temp a a b
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Blocks and Compound Statements

• Blocks begin with the left brace and end with
  the right brace
• Blocks are not terminated with a semicolon

temp a a b b temp
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Expressions

• Anything that evaluates to a value is an
  expression.

3.2 // returns the value 3.2 PI // float
const that returns the value 3.14 SecondsPerMinute
// int const returns 60 x a b // returns x
a b y x a b // assigns the return
value to y // a statement, but not an
expression
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Mathematical Operators - /

• Addition (), subtraction (-), multiplication
  (), division (/), modulus ()

x 5 2 // x is 7 x 5 - 2 // x is 3 x
5 2 // x is 10 x 5 / 2 // x is 2 x 5
2 // x is 1 x (double) 5 / 2 // x is 2.5
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Combining the Assignment and Mathematical
Operators
int MyAge 5 int temp temp MyAge
2 MyAge temp MyAge MyAge 2 MyAge 2

• also -, /, ,

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Increment and Decrement
C C 1 C 1 C C C - 1 C - 1 C- -

• There is no equivalent , //,

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Prefix and Postfix
int a, b, x 5 a x // x is 6, a is 5 b
x // x is 7, b is 7
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Precedence

• See Operator Precedence, Appendix A

x 5 3 8 // x is 64, or x is 29? x (5
3) 8 // x is 64 x 5 (3 8) // x is
29 x 5 3 8 // is higher precedence
than // thus x is 29
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Nesting Parentheses

• It is ok to nest parentheses to clarify precedence

X a ((b c) / ((d - e) f))
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Truth

• 0 is false, false is zero
• all other values are true, true is not zero
• Relational operators evaluate as true (1) or
  false (0) , !, gt, gt, lt, lt

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The Relational Operators
Equals 1 1 (true) 1 2
(false) Not Equals ! 1 ! 1 (false) 1
! 2 (true) Greater Than gt 1 gt 1 (false) 1
gt 2 (false) 2 gt 1 (true) Greater Than gt 1
gt 1 (true) 1 gt 2 (false) or Equals 2 gt 1
(true) Less Than lt 1 lt 1 (false) 1 lt 2
(true) 2 lt 1 (false) Less Than lt 1 lt
1 (true) 1 lt 2 (true) or Equals 2 lt 1 (false)
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The if StatementControls Program Flow

• If the expression is true, the following
  statement is executed.
• If the expression is false, the following
  statement is not executed.

if (BigNumber gt SmallNumber) BigNumber
SmallNumber cout ltlt BigNumber ltlt BigNumber
ltlt endl cout ltlt SmallNumber ltlt SmallNumber
ltlt endl
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Indentation Styles
if (expression) statements if
(expression) statements if
(expression) statements
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Indentation Styles
if (expression) statements if
(expression) statements if
(expression) statements
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else
if (FirstNumber gt SecondNumber) cout ltlt
FirstNumber is bigger\n else cout ltlt
FirstNumber is not bigger\n
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Advanced if else Statements
if (expression1) if (expression2) statement1
else if (expression3) statement2 else
statement3 else statement4
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Advanced if else Statements
if (expression1) if (expression2) statement1
else if (expression3) statement2 else
statement3 else statement4
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Advanced if else Statements
if (expression1) if (expression2) statement1
else if (expression3) statement2 else
statement3 else statement4
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Advanced if else Statements
if (expression1) if (expression2) statement1
else if (expression3) statement2 else
statement3 else statement4
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Advanced if else Statements
if (expression1) if (expression2) statement1
else if (expression3) statement2 else
statement3 else statement4
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Advanced if else Statements
if (expression1) if (expression2) statement1
else if (expression3) statement2 else
statement3 else statement4
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Advanced if else Statements
if (expression1) if (expression2) statement1
else if (expression3) statement2 else
statement3 else statement4
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Logical Operators
AND expression1 expression2 OR expres
sion1 expression2 NOT ! !expression1
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Logical AND
if ((x 5) (y 5))

• expression1 expression2
• if both expressions are true, then the logical
  AND statement is true
• if either expression is false, then the logical
  AND statement is false
• if both expressions are false, then the logical
  AND statement is false

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Logical OR
if ((x 5) (y 5))

• expression1 expression2
• if either expression is true, then the logical
  OR statement is true
• if both expressions are true, then the logical OR
  statement is true
• if both expressions are false, then the logical
  OR statement is false

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Logical NOT
if (!(x 5))

• !expression
• if the expression is true, then the logical NOT
  statement is false
• if the expression is false, then the logical NOT
  statement is true

x !0 // the value of x is 1 x !1 // the
value of x is 0
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Conditional (Ternary) Operator ?
z (x gt y) ? x y

• expression1 ? expression2 expression3
• if expression1 is true, return the value of
  expression2
• if expression1 is false, return the value of
  expression3