If Statements

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• Misc
  • Colloquium this afternoon
    • 4:00 - 5:00, Newton 201
    • “Bodybuilding! ... for Mathematicians” + career reflections
    • Extra credit for summaries
• Questions?
  • elseif vs if-else?
    • Multiway vs 2-way conditionals
      

      if a
          statement1    % done if a true
      else
          statement2    % done if a false
      end
      
      if a
          statement1    % done if a true
      elseif b
          statement2    %done if a false and b true
      elseif c
          ...
      else            
          statementn    % done if none are true
      end

• If Statements
  • Sections 4.1 - 4.3
    • Use condition to choose to do something or not
      • e.g., if negative, equal, greater than 0, etc.
    • Can also choose between 2 actions or multiple actions
    • Can nest if statements to choose between multiple actions
  • Idioms
    • Process some data and ignore others, e.g., count negative numbers
      

      %% Count negative numbers input by user
      x = input( 'Enter a number ' );
      if x < 0
          negatives = negatives + 1;
      end

    • Process data in 2 different ways, e.g., absolute value
      

      %% Print absolute value of user input
      x = input( 'Enter a number ' );
      if x >= 0
          fprintf( 'The absolute value of %f is %f\n', x, x );
      else
          fprintf( 'The absolute value of %f is %f\n', x, -x );
      end

    • Process data in multiple ways, e.g., classify integers by how close to a multiple of 3 they are
      

      %% Classify numbers as close to multiples of 3
      x = input( 'Enter a number ' );
      if x/3 == floor(x/3)
          fprintf( '%f is a multiple of 3\n', x );
      elseif x/3 - floor(x/3) < 0.5
          fprintf( '%f is just past a multiple of 3\n', x );
      elseif x/3 - floor(x/3) > 0.5
          fprintf( '%f is almost a multiple of 3\n', x );
      else
          fprintf( '%f is exacty halfway between multiples of 3\n', x );
      end

      • floor(x) = ⌊x⌋ = greatest integer ≤ x
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