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Lab 24: Test 3 Review

As usual, create a directory to hold today's files. All programs that you write today should be stored in this directory. 

$ cd ~/cs120/labs
$ mkdir lab24 
$ cd lab24

Coding Review Questions

Divide String

Write a function called divide_string(a_string), which takes a string as a parameter. Your function should return a string, which is the second half of characters from a_string followed by the first half of characters. 







  
Sum Letters




  Write a function called weird_strings(a_string), which
  takes a
  string as a parameter.  Your function should return smallest slice
  of the
  first \(n\) characters from a_string, such that the sum of
  the
  ordinal values of the characters in slice is greater than or equal
  to
  \(220\).  Assume that all strings given to your function will be
  long
  enough to obtain such a slice, and your function should ignore
  capitalization.


  

    
  

  

    
  

  










Base Conversion



  We can convert from binary to decimal values, however, there are
  many instances where we want to go the other direction.  Having a
  binary number can assist in computing permutations of a set, as well
  as many other practical applications.  Today, you will write a
  function that will perform the computation the opposite direction.




Details



  Write a function called convert_to_binary(integer)
  in a file called base_conversion.py.  This function takes
  one integer parameter: the decimal number to convert to base-2.
  This function should 
  return a string representation of integer in the
  base-2.




  Make sure your program handles all necessary cases gracefully.  What
  additional test cases should you check?




Sample Test Cases



  
    

      Function Call
      Expected Output
    

  
  
    

      convert_to_binary(2)
      10
    

    

      convert_to_binary(3)
      11
    

    

      convert_to_binary(5)
      101
    

  




Hint



  
  

    
    
      
  • 
	
    
	  You are going to use the accumulator pattern to accumulate a
	  string that represents the input integer converted to the
	  specified base.
        
    
      
    • 
      
  • 
        
    
	  Inside the loop calculate the quotient and remainder of
	  dividing the input integer by the new base.  The remainder
	  is a place value (a single bit) of the converted integer and
	  should be accumulated.
        
    
      
    • 
      
  • 
	
    
	  The quotient of the previous iteration is the input integer
	  of the next iteration.  At the bottom of the loop, update
	  the input integer to be the quotient.
	
    
      
    • 
  






  
Challenge

  

    

      Another very popular numeric system is known as hexadecimal.
      hexadecimal is simply a base 16 number system.  However, we only
      have 10 "numeric" digits to work with in our number system.  We
      typically get around this by using letters for the rest of the
      numbers.  So, 'A' is used to represent the digit 10,
      'B' for the digit 11, and up to 'F' representing
      the digit 15.
    

    

      Add a function called convert_to_hexadecimal(integer)
      function that converts the parameter to base 16.  Remember that
      since the ASCII values of the upper case characters are
      sequential, you don't need 6 conditionals to handle the
      characters in a hexadecimal number.