CPSC 110 Fall 2011 Quiz 2 Practice Questions

    Instructions: The first three problems ask you to read a Pseudocode algorithm. Trace through each of them by hand, keeping track of the variables, to determine the answer to the question.

  1. Suppose you have a global variables named Var and N. What value would Var have after the following Pseudocode segment?
    ProblemSolution
    Set Var to 100
Set N to 3
Set Var to Var - N
If Var < 97 then do:
   Set Var to 0
else-do:
   Set Var to 1

    Var   N   Var < 97
------------------
100   3     
97    3     false
1                    So the answer is Var = 1 after the algorithm runs
  2. What values would Var and N have after the following Pseudocode segment?
    ProblemSolution
    Set Var to 1
Set N to 0
While Var < 16 do:
   Set Var to Var * 2
   Set N to N + 1

    Var   N   Var < 16
------------------
1     0     true
2     1     true
4     2     true
8     3     true
16    4     false  So the answer is Var = 16 when the loop finishes
  3. Consider the following procedure. What value would Var have after the DoSomethingInteresting procedure is called?
    ProblemSolution
    # Comment: A mystery procedure in Pseudocode

To DoSomethingInteresting
  Set Var to 0
  Set N to 1
  While N < 10 do:
      Set Var to Var + N
      Set N to N + 2

    Var   N   N < 10
------------------
0     1     true
1     3     true
4     5     true
9     7     true
16    9     true
25    11    false   So Var = 25 after this procedure is called.
                    The procedure computes the sum of the odd numbers between 1 and 10




    Instructions: The next three problems ask you to write a Pseudocode algorithm. Model your answers after the Pseudocode algorithms in the first there questions.

  4. Suppose you have the global variables A, B, and C. Write a Pseudocode algorithm that will add them together and store the sum in the variable Var 

    # Comment: An algorithm that adds A, B, and C giving Var

  Set Var to 0                            
  Set Var to Var + A       or  Set Var to A + B + C
  Set Var to Var + B
  Set Var to Var + C
  5. Suppose you have a variable N and a variable M. Write an if/else algorithm that tests whether N and M are equal. If they are, set the variable Var to 1. Otherwise set it to 0. 

    # Comment: Sets Var to 1 if M=N or to 0 of M <> N

  If M = N then do:
     Var = 1
  else=do:
     Var = 0

  6. Suppose you have variables named Var and N. Write a pseudocode loop algorithm that will use these two variables to multiply Var by itself 10 times. For example, if Var is 2, then your algorithm will multiply 2 * 2 * 2 ... * 2, 10 times, giving 1024.

    AlgorithmTrace
    # Comment: Multiplies Var by itself N times. 
# It is not necessary to know the value of Var, but here we let Var be 2.
# And here we need a third variable to store the result. Call it Product.

   Set Var to 2
   Set Product to 1
   Set N to 1
   While N <= 10 do:
      Set Product  = Product * Var
      Set N to N + 1

    Var      Product     N    N <= 10
--------------------------------
2        1           1     true
2        2           2     true
2        4           3     true
2        8           4     true
2        16          5     true
...      ...         ...   ...
2        512         10    true
2        1024        11    false