AP CS A Unit 3 Review

Front

Consider the following code, assuming grade is an int: Which of the following will always produce the same result as the code above, regardless of the value of grade?

Back

Answer explanation

This code will replace the original and always work the same. If the grade is less

than or equal to 75, Eh is printed. If grade is greater than or equal to 100, Great is

printed and then the rest in between will receive Good.

Front

What is output by the following code? Options: 11, 15, 31, error

Back

11

Answer explanation

The x * 3 is equal to 30 so the first if runs and increments x (which is 10) by one. Then

since 11 is smaller than 31, it will not run the second if, thus printing 11

Front

Consider the following incomplete code segment. Consider the following potential replacements for /* missing code */. Which of these replacements will cause the code segment to always print false? Assume that Math is imported correctly into our program: (int)(Math.random() * 10) + 20, (int)(Math.random() * 10) + 25, (int)(Math.random() * 10) + 30, (int)(Math.random() + 30)

Back

(int)(Math.random() * 10) + 20

Answer explanation

Math.random() returns a random value between 0 (inclusive)

and 1 (exclusive). So Math.random()*10 + 20 can give values

between 20.0 and 29.9999... By typecasting the value to an int,

the decimal values are truncated, which gives a range from 20 to

29 inclusive, meaning it never returns 30, and false is always

printed as a result

Front

Given the variables, which boolean condition is true? Options: a < b && a == b, a > b || a != b, a < b && a != b, b >= a && a >= b

Back

b >= a && a >= b

Answer explanation

This is equivalent to a == b, which is true

Front

The following if statement tests the snowfall in Alaska during the months of December, January and February. Assume low represents a threshold determined to be the least amount of snow required to be normal and high represents a threshold determined to be the most amount of snow required to be normal and snow represents the amount of snow in inches for that month. All variables are doubles. It could be replaced with:

Back

Answer explanation

This solution properly splits up the compound boolean expression and created two

nested if/else statements

Front

The following truth table matches which boolean condition?
Options: A && ( A || B ), A && ( A && B ), !A && ( A || !B ), A || ( A || B )

Back

A || ( A || B )

Answer explanation

This is equivalent to A || B which the truth table reflects

Front

To test if a grade (represented by the double variable g) is a B (between 80 - inclusive - and 90 exclusive) you would use the following if statement: What set of three symbols correctly fills in the blanks in the order they appear? Options: >=, &&, <, >=, ||, <, >, ||, <=, <=, &&, >

Back

>=, &&, <

Answer explanation

We want inclusive of the lower bound and exclusive of the upper bound, so we

need to use >= and <, and we need both conditions to be true so we use &&

Front

The result of evaluating the expression is best described as: always true, always false, true only when x is true and y is true, true only when x and y have the same values, true only when x and y have different values

Back

true only when x and y have different
values

Answer explanation

(x||y) - x or y must be true; && - and the next expression must be true; !(x&&y) - x and y can not both be true

Front

Consider the following code fragment, assume val is an int: Which of the following code fragments would have the same effect? if (!(val == 50 || val < 0)), if (val == 50 || val > 0), if (val == 50 || val < 0), if (val == 50 && val < 0)

Back

if (val == 50 || val < 0)

Answer explanation

When val is a negative value or 50, it should evaluate to true, this is the

proper use of De Morgan’s law (&& will change to ||)

Front

Which of the following is an example of short circuit evaluation? if x * y > 1 is false it evaluates y != 0, if x * y > 1 is false it doesn't evaluate y != 0, if y != 0 is false it doesn't evaluate x * y > 1, if y != 0 is true it doesn't evaluate x * y > 1

Back

if y != 0 is true it doesn't evaluate x * y > 1

Answer explanation

This is an OR statement, so if either half is true, the

statement is true. If the first half is true, it doesn’t need

to evaluate the second half