Types,%20Truth,%20and%20Expressions

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Types, Truth, and Expressions

• Intro to Computer Science
• CS1510, Section 2
• Dr. Sarah Diesburg

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What type(s) would we use

• To represent your
• Weight
• Height
• Age
• Name
• Class status (freshman, sophomore, etc)
• Gender
• If you owe the university money
• If you are taking classes this semester

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Yesterdays Lab Main Concept Review

• First we looked at the idea of Conditionals and
  the basic six operators
• Less than lt
• Greater than gt
• Equal to (Not the same as )
• Not equal to !
• Less than or equal to lt
• Greater than or equal to gt

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Yesterdays Lab Main Concept Review

• The results of a conditional operator is always a
  Boolean value.
• Meaning ???
• Either True or False

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Boolean Expressions

• George Booles (mid-1800s) mathematics of
  logical expressions
• Boolean expressions (conditions) have a
  value of True or False
• Conditions are the basis of choices in a
  computer, and, hence, are the basis of the
  appearance of intelligence in them.

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What is True, and What is False

• True any nonzero number or nonempty object. 1,
  100, hello, a,b
• False zero number or empty object. 0, ,
• Special values called True and False, which
  are just stand-ins for 1 and 0. However, they
  print nicely (True or False)

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Boolean Expression

• Every boolean expression has the form
• expression booleanOperator expression
• The result of evaluating something like the above
  is just True or False.
• Evaluating a boolean operation is a binary
  operation
• if (altb) has two operands in expression
• However, remember what constitutes True or False
  in Python!
• If (a) will evaluate to True if a is non-zero!

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Relational Operators

• Relational Operators have low preference
• 5 3 lt 3 2
• (5 3) lt (3 - 2)
• 8 lt 1
• False

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Selection

• Then we looked at how conditionals are applied in
  selection statements.
• Selection is how programs make choices, and it is
  the process of making choices that provides a lot
  of the power of computing

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Python if Statement

• if boolean_expression
• suite
• evaluate the boolean_expression (True or False)
• if True, execute all statements in the suite

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Warning About Indentation

• Elements of the suite must all be indented the
  same number of spaces/tabs
• Python only recognizes suites when they are
  indented the same distance
• You must be careful to get the indentation right
  to get suites right.

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Python Selection, Round 2

• if boolean expression
• suite1
• else
• suite2

• The process is
• evaluate the boolean
• if True, run suite1
• if False, run suite2

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Chained Comparisons

• In python, chained comparisons work just like you
  would expect in a mathematical expression
• Given myInt has the value 5
• 0 lt myInt lt 5
• True
• 0 lt myInt lt 5 gt 10
• False

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Compound Expressions

• Logically 0 lt X lt 3 is actually(0 lt X) and (X lt
  3)
• Logical Operators (lower case)
• and
• or
• not