7 - Control Palooza

ucla | CS 131 | 2023-11-29 15:09

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Table of Contents

• Expressions, Associativity, and Order of Eval
• Short-Circuiting
• Control Statements
  • Unconditional Branching
    • GOTO
    • BREAK and CONTINUE
  • Conditionals
  • Switch statements
• Loops
  • Counter-controlled iteration
  • Collection-controlled iteration
  • Conditional Looping
• Iteration
  • Iterable objects
  • Iterators
    • With Traditional Classes:
    • With Generators (True Iterators)
  • First Class Functions for Iteration

Expressions, Associativity, and Order of Eval

• C++ is not deterministic in the evaluation of the terms of an expression, e.g. evaluating a function in an arithmetic expression or evaluating a function passed as a parameter
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  • Instead, it leaves it to the compiler to optimize
  • so, we should write pure code that does not introduce possible side effects
• most mathematical expressions are left-associative and are returned in normal mathematical order, but there are some exceptions
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    Short-Circuiting

• The program will optimize boolean expressions so that it will “short circuit” and only evaluate as few expressions as possible, left-to-right
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• short-circuiting is expected but not guaranteed, depends on the lang

  Control Statements

  Unconditional Branching

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  GOTO

• assign labels to lines of code
• jump to the label/line
• can introduce undefined behavior if not careful
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BREAK and CONTINUE

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• new features allow you to break from labeled loops and continue to labeled loops
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Conditionals

• IF was first used in Fortran to jump to line numbers based on flags for whether the number is negative, zero, or positive
  • 
• Ternary operator is if else in 1 line w 3 operands
  • 
• null coalescing operator: if true then pas s the var else pass alt
  • 
• safe navigation operator, checks if the navigation is valid else entire statement is false/null
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    Switch statements

• started in fortran with a goto and line numbers
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  Loops

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  Counter-controlled iteration

• iterates over a range of values (foreach)
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  Collection-controlled iteration

• iterates over the elements in an iterable objects
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  Conditional Looping

• while and do while
• do always runs the 1st iteration

Iteration

• Looping/iteration through an iterable object
• these are the types of loops:

  Iterable objects

• an iterable object is an object that can be iterated over using an iterator: a collection, list, sequence, range, etc.
• we can iterate using iterators or first class functions
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  Iterators

• an object that allows the enumeration of an iterable object’s values without exposing the underlying representation
• 
• iterators are typically distinct from the value they enumerate, but to the programmer, it is an abstraction so we can not know if it actually caches or just points
• iterators are distinct from the iterable object so we can have multiple iterators for the same iterable
• iterators are generated by the iterable object and may become invalid over execution (e.g., if you delete an object in a vector in C++, the iterator becomes invalid )
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• Iterators are implemented via:

  With Traditional Classes:

• Implementing a container:
• Implementing a range:

  With Generators (True Iterators)

• A generator in python:
  • 
  • 
• Iterating through a generator:
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First Class Functions for Iteration

• we can create a simple mapping member function that does a for each loop and calls the passed function
•