Absolute C++ 5th Edition by Walter Savitch - Test Bank

Chapter 2 - Test Questions

These test questions are true-false, fill in the blank, multiple choice, and free form questions that may require code. The multiple choice questions may have more than one correct answer. You are required to mark and comment on correct answers.. Mark all of the correct answers for full credit. The true false questions require an explanation in

addition to the true/false response, and, if false, also require a correction.

True False:

1.     The  if, while and for statements control only one statement.

Answer: True

Explanation: The one statement may be a block (statements that are enclosed with curly braces { }) or a simple statement.

2.     Given the declaration

int x = 0;

The following expression causes a divide by zero error:

(x !=0) || (2/x < 1);

Answer: False.

Explanation: The || operator uses short-circuit evaluation. The first member of this expression is true; the truth value of the complete expression can be determined from this; consequently, the second expression is not evaluated. There is no divide-by-zero error.

3.     Suppose we have these declarations,

int x = -1, y = 0, z = 1;

This Boolean expression is correct and it does what the programmer intends.

x < y < z

Answer: False

Explanation: Unfortunately, the expression compiles without error and runs. The < operator associates (groups) left to right, so the expression evaluates as

(x < y) < z

The left hand expression evaluates to true, which, if compared to a numeric type, converts to 1. When compared to 1, this is false. What the programmer intends, expressed as mathematacs might is -1 < 0< 1, a result that is clearly true.

4.     You want to determine whether time has run out. The following code correctly implements this.

            !time > limit

Answer: False.

Explanation: The expression always evaluates to false. This cannot be what the programmer intended. The compiler doesn’t catch the problem because the code is legal, correct C++. Corrected code is !(time > limit)

Code execution proceeds as follows: The operator ! takes a bool argument. It returns the opposite bool value. The value of time is converted to a bool. The value of time is certainly nonzero, hence !time is !true, i.e., false. The > compares this result with a numeric value, limit, (an int or perhaps some kind of floating point). The value on the left (false) is converted to a 0 value of that type. The value of limit is unlikely to be a negative number and we are concerned about time running out, so it is unlikely that time is zero. Consequently, the inequality becomes 0>limit, where limit is nonzero. This is false.

5.     The value of count is 0; limit is 10. Evaluate: 

(count == 0)&&(limit < 20)

Answer: true

6.     The value of count is 0; limit is 10. Evaluate:

count == 0 && limit < 20

Answer: true