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.