CISC-1600-E01 Midterm Postmortem

Wrong answers I received are in yellow.

  1. What is the value of each of the following C++ expressions? 
    1. 	1 - 2 - 3

      The value is −4, because - (subtraction) has left-to-right associativity (line 6 in the table).

      The answers I received included 

      -2


    2. 	(1 - 2) - 3

      The value is −4, because an operator in parentheses is executed before the ones outside the parentheses.

      The answers I received included the following: 

      4

      error due to closing parenthesis

      2

    3. 	1 - (2 - 3)

      The value is 2, because an operator in parentheses is before the ones outside the parentheses.

      The answers I received included the following: 

      0

      2

  2. How many operators are there in each of the following C++ expressions? Number the operators in the order in which they are executed. For example, in the first expression, the * is number 1, and the + is number 2. 
    1. 	a + 10 * b
	  2    1                  Two operators, at lines 5 and 6 in the table.

    2. 	-a * 10 - b
	1  2    3                 Three operators, at lines 3, 5, and 6 in the table.
      Answers I received included the following: 
      * is 1, - is 2, - is 3

      * is 1, - is 2

    3. 	cout << a + 10 * b
	     3    2    1          Three operators, at lines 5, 6, and 7 in the table.

    4. 	cout << 1 - 2 - 3
	     3    1   2           Three operators, with left-to-right associativity (line 6 in the table).

    5. 	cout << a << b << c << "\n"
	     1    2    3    4     Four operators, with left-to-right associativity (line 7 in the table).

      Answers I received included the following: 

      1.  << out operator before comparison
2.  comparison
3.  c5 logical and
4.  << output comparison after operator


    6. 	z = y = x = 10
	  3   2   1               Three operators, with right-to-left associativity (line 16 in the table).
      Answers I received included the following: 
      = is 1, = is 2, = is 3

  3. How many characters does this C++ statement output? 
    	cout << "\n";

    The answer is 1 character. (That character is the newline character).

    Answers I receieved included 

    this is a newline character
cout is "\n" because it's in quotes
or until conditions for a for loop is met.

    80 "because a line is 80 characters."

    Zero

    0

  4. What does each of the following C++ examples output?
    See assignment.C and increment.C. 
    1. 	int i {10};
	i *= 2;    //means i = i * 2;
	cout << i << "\n";

      20

      Answers I received included the following: 

      10
20
30
40 ...

      	int i {10}; = 1033;
	int i *= 2;
	cout << i << "\n";

	The output will be 2066, as 1033 * 2 = 2066

    2. 	int i {10};
	i /= 2;     //means i = i / 2;
	cout << i << "\n";

      5

      Answers I received included the following: 

      10
5
2.5 ...

      	int i {10}; = 18;
	i /= 2;
	cout << i << "\n";

	The output will be 9, as 18/2 = 9

      output = .20

    3. 	int i {10};
	++i;    //means i = i + 1;
	cout << i << "\n";

      11

      Answers I received included the following: 

      11, 12, 13, 14 ...

      10
11
12
13 ...

      	int i {10}; = 10;
	++i;
	cout << i << "\n";

	The output will be 100, as the 10 is printed
	twice, which the isaline will be 10 * 10 = 100

      1, 2, 3 4 5 6 7 8 9 10

  5. Assume you already have a variable named i, of data type int. In the following parentheses, write a C++ expression whose value is true if i is even, false if i is odd.
    See our first example of an if inside a for loop, product4.C. 
    	if (i % 2 == 0) {    //if i divided by 2 has a remainder of 0
		cout << i << " is even.\n";
	} else {
		cout << i << " is odd.\n";
	}
    Answers I received included the following: 
    	if (1 => 1 * 2) {

    	if (int i {2}

    	if (i % != 2) {

    	if (n > 0) {

    	if (i % 2 = 0) {

    	if (i % 2 = 0) {

    	if (int i % 2 == 0) {

    	if (i {2} i * 2;) {

    	if (i / 2) {

    	if (i <= 10) {

  6. Assume you already have a variable named pennies, of data type int, containing the number of pennies you have. Define two more variables, named dollars and cents, of type int. Initialize dollars to the number of dollars that you have in this pile of pennies. Initialize cents to the number of remaining cents. (Hint: the initial value of cents must be a number in the range 0 to 99 inclusive.)
    See remainder.C. 
    	int dollars {pennies / 100};
	int cents   {pennies % 100};
    Answers I receieved included the following: 
    	int dollars {0};
	cin >> dollars;
	int cents {0};
	cin >> cents;

    	int dollars {0};                 int cents {0};
	{(cents / 100) % = cents;}
	cout <<

    	for (int d {0} d <= n
	int cent {0} << 99

    	int dollars = pennies / 100;
	int cents = pennies % 100;

    	int pennies(0);
	int dollars {0}; pennies / 100;
	int cents {0};   pennies % 100;

    	double dollars {0.0};
	double cents {0.0};

    	Dollar = Pennies / 100
	cents = Pennies %

    	int dollars {20}       int dollars {20} -
	int cents {99}
	int pennies {1}

    	Int Pennies {150}
	Int dollars {Pennies <= 100}
	Int Cents   {Pennies < 50}

    	int pennies {100}
	int dollars (pennies / 100)
	int cents   (pennies % 100)

    	int dollars {0};
	int cents {0};
	dollars = pennies / 100;
	cents   = pennies % 100;
  7. What is output by each of the following C++ for loops?
    See for2.C. 
    1. 	int n {3};

	for (int i {0}; i < n; ++i) {
		cout << i << "\n";
	}

      0
1
2

      Answers I received included the following: 

      1, 2, 3

      0
1
2
0
1
2 ....

      	return EXIT_SUCCESS

      1, 2.

      0
1
2
3

      1
2

      output = 1, 2

      return n {0}

    2. 	int n {3};

	for (int i {1}; i < n; ++i) {
		cout << i << "\n";
	}

      1
2

      Answers I received included the following: 

      1
2
1
2
1
2 ....

      	EXIT_SUCCESS

      2.

      1
2
3

      2

      3. output = 2,

      return 3

    3. 	int n {3};

	for (int i {0}; i <= n; ++i) {
		cout << i << "\n";
	}

      0
1
2
3

      Answers I received included the following: 

      1, 2, 3

      0
1
2
3
0
1
2
3 ...

      	return EXIT_FAILURE

      1, 2, 3

      0
1
2
3
4

      1
2
3

      output = 1, 2, 3

      n <= 0

    4. 	int n {3};

	for (int i {1}; i <= n; ++i) {
		cout << i << "\n";
	}

      1
2
3

      Answers I receieved included the following: 

      1
2
3
1
2
3 ...

      	return EXIT_FAILURE

      2, 3.

      2
3

      output = 2, 3

      n <= 3

  8. What does the following C++ code output? Draw a picture.
    See line.C and rectangle.C. 
    	for (int i {0}; i < 2; ++i) {
		for (int j {0}; j < 3; ++j) {
			cout << "X";
		}
		cout << "\n";
	}

    XXX
XXX
    Answers I received included the following: 
    XX

    X

    X
X

    XXXX
XXXX
XXXX

    XX
XX
XX

  9. What (if anything) goes wrong in the following C++ code?
    The variable i no longer exists at the time when you try to output its value. See for2.C. 
    	for (int i {0}; i < 10; ++i) {
		cout << i << "\n";
	}

	cout << "After the loop is over, the value of i is " << i << "\n";

    The answers I received included the following: 

    There is nothing wrong here, the loop
will print 'X' 10 times, and once the
loop finishes, it will print the final
value of i, which will be 10.  The
output will be
After the loop is over the value of i=10 XXXXXXXXXX

    Nothing.

    All good.

    nothing wrong

    EXIT_FAILURE

    This cout [the last one] should be in the for loop.  Because it's not the
line wont be iterated with the rest of the loop.  Only printing
one value not 9

    Everything appears in order.

  10. What (if anything) goes wrong in the following C++ code?
    The variable money is born holding unpredictable garbage. When we try to output its value after the 10 multiplications, it holds unpredictable garbage that is somewhat larger.
    For the 10 repetitions (“iterations”) of the for loop, see for2.C.
    For the *= operator, see assignment.C again. 
    	double money;

	//Increase the money by 6 percent each year, for 10 years.

	for (int year {0}; year < 10; ++year) {
		money *= 1.06;   //means money = money * 1.06
	}

	cout << "After 10 years, the money has grown to " << money << "\n";

    The answers I received included the following: 

    The thing that goes wrong here is
that it would count up to 9.

    return EXIT_FAILURE was not used

    because it will only go
up to year 9.

    There is no variable after the times
sign so the computer inputs garbage.

    The value of i will always be less than 10.

    The amount of money won't be anything due
due to the sentence being out of the for loop.

    The problem is that the program will only run to 9 years.
If you want 10 years, change the value to 11.

    nothing goes wrong
but the initialization
of money is outdated
and has garbage
at first.
  11. Will the following two pieces of C++ code always produce the same output, no matter what values are in the variables harris and trump?
    No. If the variables harris and trump hold the same value, then the two pieces of code will produce different outputs. 
    1. 	if (harris < trump) {
		cout << "Harris lost.\n";
	}

	if (harris > trump) {
		cout << "Harris won.\n";
	}

    2. 	if (harris < trump) {
		cout << "Harris lost.\n";
	} else {
		cout << "Harris won.\n";
	}

      Answers I receieved included 

      Yes.

      Yes
Yes

      No same output

      Yes!
  12. Assume you already have a variable named dollars, of data type int, containing the number of dollars you have. Write C++ code that will output an English sentence such as 
    You have 1 dollar.
    or 
    You have 5 dollars.
    to show the value of this variable. In this sentence, the last word must be singular (“dollar”) if the value of the variable dollar is 1, plural (“dollars”) otherwise.

    Be sure to output a space on both sides of the number: you don’t want to output something like 

    You have 5dollars.
    As shown above, the English sentence should end with a period. Please output one newline character after the sentence. Output the newline without using endl. 

    	if (dollars == 1) {
		cout << "You have " << dollars << " dollar.\n";
	} else {
		cout << "You have " << dollars << " dollars.\n";
	}

    	cout << "You have " << dollars;

	if (dollars == 1) {
		cout << " dollar.\n";   //singular
	} else {
		cout << " dollars.\n";  //plural
	}

    	cout << "You have " << dollars << " ";

	if (dollars == 1) {
		cout << "dollar";   //singular
	} else {
		cout << "dollars";  //plural
	}

	cout << ".\n";   //Period at end of sentence, followed by newline.

    	cout << "You have " << dollars << " dollar";

	if (dollars != 1) {   //is not equal to 1
		cout << "s";  //Make the noun plural.
	}

	cout << ".\n";   //Period at end of sentence, followed by newline.

    Answers I received included the following: 

    	if (dollars == 1) {
		cout "1 dollar\n.";
	else {
		cout "5 dollars\n.";

    	cout << "dollar " << 5 << \n";

    	You have 5 dollars.\n;

    	dollar == 1
		cout << You have " << dollar << "dollar.\n";
	} else {
		cout << You have " << dollar << dollar.\n";
	}

    	cout << "you have " << dollars << " dollars.\n";

    	int i {0};

	cout << "you have " << i << "dollars.\n";
	if i < 2;
		cout << "you have " << i << "dollar.\n";

    	cout << "you have " << dollars << else if cout << "dollar" >>

	cout << "you have " << dollars << if (double) cout << "dollars" >>

	cout << "you have " << dollars << "\n";

    	if (dollars == 1) {
		cout << "You have " << dollar >> "dollar"\n.";
	}

	if (dollar > 1) {
		cout << "You have << dollar >> "dollars"\n.";
	}

    	if (dollars : {1}; i > 1; ++i) cout << "You have __ dollars." << i << ".\n";

    	Int dollar {1}
	cout << "You have " << dollar << "__ dollar.\n"

	Int dollars {-5}
	cout << "you have " << dollars << "__ dollars.\n";

    	if (dollars = 1) {
		cout << You have 1 dollar.\n";
	} else {
		cout << You have " << dollars << " dollars\n";
	}
  13. What (if anything) goes wrong in the following C++ code?
    The following code will never output the second error message, even if the user claims to have been born in a clearly impossible year like 1776.
    The && (“and”) should have been || (“or”). See the && in and2.C. 
    	cout << "In what year were you born?\n";
	int year {0};
	cin >> year;

	if (!cin) {
		cerr << "Sorry, that wasn't a number.\n";
		return EXIT_FAILURE;
	}

	if (year < 1924 && year > 2024) {
		cerr << "Sorry, you could not have been born then.\n";
		return EXIT_FAILURE;
	}

    The answers I received included: 

    The computer reads our C++
program from top to bottom.  Not
defining, declaring, and initializing the
variable at the very top
of our program will not allow
our program to execute.
Ans: No, this C++ program won't run.

[Comment by teacher:
What the student wrote was true in the language C,
but is no longer true in the language C++.]

    int year {0};
should have been
declared first -
and then the
output cout <<

    No else was used
between if and if
  14. What is a computer?
    A computer is a machine that follows instructions.

    Answers I receieved included 

    High performance application

    A machine

    list instructions
  15. What is a program?
    A program is the list of instructions you put into the computer.

    Answers I receieved included 

    It's a series of code that is built for a function.

  16. Will the following two pieces of C++ code always produce the same output, no matter what value is in the variable hour?
    Yes.
    (If you disagree with this answer, the burden of proof is on you. Please tell me a value for hour that would cause the two pieces of code to produce different outputs.) 
    1. 	if (hour >= 12) {
		if (hour >= 12 + 5) {
			cout << "Good evening.\n";
		} else {
			cout << "Good afternoon.\n";
		}
	} else {
		cout << "Good morning.\n";
	}

    2. 	if (hour < 12) {
		cout << "Good morning.\n";
	} else if (hour < 12 + 5) {
		cout << "Good afternoon.\n";
	} else {
		cout << "Good evening.\n";
	}

    Answers I received included 

    NO

    NO same outputs

    This output [box (b)] would not be the
same as (a) due to the way the
nested if statements are set up.

Table of precedence and associativity
for the C++ operators we have covered so far

An excerpt from this table.

Precedence Operator Description Associativity
3   -a  
  ++a  
negation (as in “negative 5”)
increment (i.e., “add 1”) 		right-to-left
5   a*b     a/b     a%b   multiplication, division, and remainder left-to-right
6   a+b     a-b   addition, subtraction left-to-right
7   cout<<x     cin>>x   output, input left-to-right
9   a<b     a<=b  
  a>b     a>=b   		is less than, is less than or equal to,
is greater than, is greater than or equal to 		left-to-right
10   a==b     a!=b   is equal to, is not equal to left-to-right
14   a&&b   and left-to-right
15   a||b   or left-to-right
16   a=b  
  a+=b     a-=b     a*=b     a/=b     a%=b   		assignment
(change the value of a variable) 		right-to-left