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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 of i and n after the code is executed?
      Answer: i is 11, and n is 0.

    2. Question: What are the final values of i and n if instead of using the postfix increment operator (i++), you use the prefix version (++i))?
      Answer: i is 11, and n is 1.

  3. Question: To invert the value of a boolean, 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: "If someCondition is true, assign the value of value1 to result. Otherwise, assign the value of value2 to result."

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 code System.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.

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