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Answers to Questions and Exercises: Operators

Answers to Questions

1. Consider the following code snippet:

   arrayOfInts[j] > arrayOfInts[j+1]

   Question: What operators does the code contain?
   Answer:>,+
   
   
2. Consider the following code snippet:

   int i = 10;int n = i++%5;

   1. Question: What are the values ofi andn after the code is executed?
      Answer:i is 11, andn is 0.
      
      
   2. Question: What are the final values ofi andn if instead of using the postfix increment operator (i++), you use the prefix version (++i))?
      Answer:i is 11, andn is 1.
      
      
3. Question: To invert the value of aboolean, which operator would you use?
   Answer: The logical complement operator "!".
4. Question: Which operator is used to compare two values,= or== ?
   Answer: The== operator is used for comparison, and= is used for assignment.
5. Question: Explain the following code sample:result = someCondition ? value1 : value2;
   Answer: This code should be read as: "IfsomeCondition istrue, assign the value ofvalue1 toresult. Otherwise, assign the value ofvalue2 toresult."

Exercises

1. Change the following program to use compound assignments:

   class ArithmeticDemo {    public static void main (String[] args){                  int result = 1 + 2; // result is now 3        System.out.println(result);        result = result - 1; // result is now 2        System.out.println(result);        result = result * 2; // result is now 4        System.out.println(result);        result = result / 2; // result is now 2        System.out.println(result);        result = result + 8; // result is now 10        result = result % 7; // result is now 3        System.out.println(result);    }}

   Here is one solution:

   class ArithmeticDemo {    public static void main (String[] args){        int result = 3;        System.out.println(result);        result -= 1; // result is now 2        System.out.println(result);        result *= 2; // result is now 4        System.out.println(result);        result /= 2; // result is now 2        System.out.println(result);        result += 8; // result is now 10        result %= 7; // result is now 3        System.out.println(result);    }}

2. In the following program, explain why the value "6" is printed twice in a row:

   class PrePostDemo {    public static void main(String[] args){        int i = 3;        i++;        System.out.println(i);    // "4"        ++i;                             System.out.println(i);    // "5"        System.out.println(++i);  // "6"        System.out.println(i++);  // "6"        System.out.println(i);    // "7"    }}

   The codeSystem.out.println(++i); evaluates to 6, because the prefix version of++ evaluates to the incremented value. The next line,System.out.println(i++); evaluates to the current value (6), then increments by one. So "7" doesn't get printed until the next line.