Check Your Understanding

Making Decisions (Conditionals)

1. What is the value of each variable after the if statement?
   a.

    int n = 1;  
    int k = 2;  
    int r = n;  
    if (k < n) { r = k; }  
   

   b.

    int n = 1;  
    int k = 2;  
    int r;  
    if (n < k) { r = k; }  
    else { r = k + n; } 
   

   c.

    int n = 1;  
    int k = 2;  
    int r = k;  
    if (r < k) { n = r; }  
    else { k = n; } 
   

   d.

    int n = 1;  
    int k = 2;  
    int r = 3;  
    if (r < n + k) { r = 2 * n; }  
    else { k = 2 * r; } 
   

2. Explain the difference between

    s = 0;  
    if (x > 0) { s++; }  
    if (y > 0) { s++; }  
   

   and

    s = 0;  
    if (x > 0) { s++; }  
    else if (y > 0) { s++; }
   

3. Find the errors in the following if statements.
   a. if x > 0 then System.out.print(x);
   b. if (1 + x > Math.pow(x, Math.sqrt(2)) { y = y + x; } c. if (x = 1) { y++; }
   d.

      x = in.nextInt();
      if (in.hasNextInt())
      {
            sum = sum + x;
      }
      else
      {
            System.out.println("Bad input for x"); 
      }
   

   e.

      String letterGrade = "F";  
      if (grade >= 90) { letterGrade = "A"; }  
      if (grade >= 80) { letterGrade = "B"; }  
      if (grade >= 70) { letterGrade = "C"; }  
      if (grade >= 60) { letterGrade = "D"; }
   

4. What do these code fragments print?
   a.

      int n = 1;  
      int m = -1;  
      if (n < -m) { System.out.print(n); }  
      else { System.out.print(m); }
   

   b.

      int n = 1;  
      int m = -1;  
      if (-n >= m) { System.out.print(n); }  
      else { System.out.print(m); }
   

   c.

      double x = 0;  
      double y = 1;  
      if (Math.abs(x - y) < 1) { System.out.print(x); }  
      else { System.out.print(y); }
   

   d.

      double x = Math.sqrt(2);  
      double y = 2;  
      if (x * x == y) { System.out.print(x); }  
      else { System.out.print(y); }
   

5. Suppose x and y are variables of type double. Write a code fragment that sets y to x if x is positive and to 0 otherwise.

6. Suppose x and y are variables of type double. Write a code fragment that sets y to the absolute value of x without calling the Math.abs function. Use an if statement.

7. Explain why it is more difficult to compare floating-point numbers than integers. Write Java code to test whether an integer n equals 10 and whether a floating-point number x is approximately equal to 10.

8. Given two pixels on a computer screen with integer coordinates (x1 , y1) and (x2 , y2), write conditions to test whether they are
   a. The same pixel.
   b. Very close together (with distance < 5).

9. It is easy to confuse the = and == operators. Write a test program with the statement
   if (floor = 13)
   What error message do you get? Write another test program with the statement
   count == 0;
   What does your compiler do when you compile the program?

10. Write pseudocode for a program that prompts the user for a month and day and prints out whether it is one of the following four holidays:
    • New Year’s Day (January 1)
    • Independence Day (August 15)
    • Christmas Day (December 25)

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