AP Computer Science Exam Question

(a) Given the following code segment:

int x = 10;
int y = 5;
int z = x++ + --y - x / y % 2;

What are the final values of x, y, and z after executing this code? Show the step-by-step evaluation of the expression.

(b) Explain the result obtained for z in the previous code segment, and list the operators used in the expression with their associativity and precedence.

Answer

(a) Evaluating the expression step-by-step:

1. Initialize variable x with value 10.

2. Initialize variable y with value 5.

3. Evaluate x++:

   • The variable x is incremented after its value is used in the expression, so its original value 10 is used.
   • After the evaluation, x becomes 11.

4. Evaluate --y:

   • The variable y is decremented before its value is used in the expression, so its original value 5 is decremented to 4.
   • After the evaluation, y becomes 4.

5. Evaluate x / y:

   • Divide the value of x (which is now 11) by the value of y (which is 4).
   • The integer division yields 2.

6. Evaluate x / y % 2:

   • The division operator / has left-to-right associativity.
   • Perform the division first: 11 / 4 equals 2.
   • Next, apply the modulo operator %: 2 % 2 equals 0.

7. Evaluate x++ + --y - (x / y % 2):

   • Replace the expressions with their evaluated values: 10 + 4 - 0.
   • The addition is performed first: 10 + 4 equals 14.
   • The subtraction is performed next: 14 - 0 equals 14.

8. Assign the value 14 to variable z.

Therefore, the final values of x, y, and z are:

• x is 11
• y is 4
• z is 14

(b) Explanation of z result and operators used:

The expression x++ + --y - x / y % 2 results in z being assigned the value 14. Here's the breakdown:

• x++ uses the post-increment operator on x, which increments it after the value is used. In this case, it evaluates to the original value of x (i.e., 10) and then increments x to 11.
• --y uses the pre-decrement operator on y, which decrements it before the value is used. In this case, it evaluates to the decremented value of y (i.e., 4).
• x / y performs integer division of x by y, resulting in the value 2.
• x / y % 2 applies the modulo operator % on the result of the division, resulting in 0.

Hence, the final expression x++ + --y - x / y % 2 can be simplified as 10 + 4 - 0, which equals 14.

Operators used in the expression with their associativity and precedence:

• Post-increment (++) and pre-decrement (--) operators have the highest precedence and right-to-left associativity.
• Division (/) and modulo (%) operators have left-to-right associativity and equal precedence.
• Addition (+) and subtraction (-) operators have left-to-right associativity and lower precedence than division and modulo.