COMP-202
Fall 2010
Midterm solutions

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Question 1
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a) 1 - 3 * (1 + 6) / 2

Operator    Context     Result
+           (1+6)       7
*                       21
/                       10
-                       -9

b) 1/2 + 8 * (1%5 - 1)

Operator    Context     Result
%                       1
-                       0
/                       0
*                       0
+                       0

c) 2.5 * 2 + (int) 0.9/0.2

Operator    Context     Result
cast                    0
/                       0
*                       5.0
+                       5.0

d) !(1 < 1) != (7%2 == 0) || 4/4/4 > 1

Operator    Context     Result
<                       false
%                       1
==                      false
!                       true
first /                 1
second /                0
>                       false
!=                      true
||                      true

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Question 2
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3*45
20
0.75

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Question 3
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Note that there are two horizontal spaces between each character, and two 
leading spaces to the left of the bottom-left '*'.

              *
           *  *  @
        *  *  *  @  @
     *  *  *  *  @  @  @
  *  *  *  *  *  @  @  @  @

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Question 4
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There are in fact 9 errors (we overlooked the one on line 17). Anyone who gets
at least 8 of the following errors should get full marks.

Line 1:           (compile-time)
Missing brace: class body not properly defined.

Line 2:           (run-time)  
Main should be main

Line 5:           (logical)   
Infinite loop "for (int p = 2; p <= 15; p--)"

Line 9, 10, 11 or 11: (compile-time)
Dangling else (due to location of {} on lines 9 and 12.

Line 17:          (logical)
1 is not prime

Line 22:          (compile-time)
num % i = 0 does not evaluate to boolean

Line 33 or 34:    (compile-time)
lastDigit is out of scope
    
Line 30 or 34:    (compile-time)
constant variable is reassigned

Line 36:          (compile-time)
Missing return statement

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Question 5
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a) The ADDRESS to the memory location that contains array {4, 3, 44, 9, 5};

b) input[0] == 4 and input[1] == 3

c) input[0] == 9 and input[1] == 0

d) 

5
9
44
3
4
-1

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Question 6.1 and 6.2
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public class LikeBookUtils{
  
  static int countValues(boolean[] boolArray, boolean target){
    int total = 0;

    for(int i = 0; i < boolArray.length; i++){
       if(boolArray[i] == target)
          total++;
    }
    return total;  

  }  

  public static int computeMostPopular(boolean[][] likeTable){
    int current = 0, max = 0, id = 0;    
        
    for(int i = 0; i < likeTable.length; i++){
      current = countValues(likeTable[i], true);
      if(current > max){
        max = current;
        id = i;
      }
    }

    return id;
  
  } 
      

}


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Question 6.3
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import java.util.Scanner;

public class PopularityAnalyzer{
  
  public static void main(String[] args){
    Scanner input = new Scanner(System.in);
    int numPeople;

    System.out.print("Enter the number of people: ");
    numPeople = input.nextInt();

    // students may assume that numPeople > 0

    boolean[][] lTable = new boolean[numPeople][numPeople];

    for(int x = 0; x < lTable.length; x++){
      for(int y = 0; y < lTable[0].length; y++) {
        if(x == y)
          lTable[x][y] = false;
        else{
          System.out.print("Person " + y + " likes Person " + x + "?");
          lTable[x][y] = input.nextBoolean();
        }
      }
    }

    System.out.print("The most popular person is: ");
    System.out.println(LikeBookUtils.computeMostPopular(lTable));

  }
      

}