Flow Control

Question 1

What is a program’s path?

Answer 1

The sequence of statements the CPU executes.

Question 2

What does “sequential flow” refer to?

Answer 2

A program that has the same path each time it is run (i.e. no logic)

Question 3

What is a halt control flow statement?

Answer 3

The most basic control flow statement; tells the program to stop running immediately.

Question 4

What is the syntax for a function which causes a halt, and what library is it defined in?

Answer 4

exit(int exitCode);

This is similar to the way ‘main’ returns an integer.

Defined in

Question 5

What is a jump control flow statement?

Answer 5

Causes the CPU to unconditionally jump to another statement.

Question 6

What are some examples of jump keywords?

Answer 6

goto, break, continue

Question 7

Describe what happens when a function cannot handle an error.

Answer 7

If an error occurs that the function can not handle, it can raise an exception, and control jumps to the nearest block of code that has declared it is willing to catch exceptions of that type.

Question 8

What is the best syntax practice when an if statement executes a single statement, as opposed to multiple statements?

Answer 8

Use a block for multiple statements {}, and no block for single statements:

if (nX > 10)
cout &laquo_space;nX;

if(nx > 10)
     {
           cout << nX;
           cout << nY;
      }

Question 9

What must the condition of an if statement be enclosed in?

Answer 9

(parentheses)

Question 10

What is a “dangling else”, and how can they be avoided?

Answer 10

When nesting if/else statements, it can become unclear which if belongs to which else; these can be made less ambiguous by always using blocks when nesting statements. Without a block, the else simply would attach to the nearest if:

if (nX > 10)
{
if (nX < 20)
cout &laquo_space;nX &laquo_space;“is between 10 and 20” &laquo_space;endl; }
else // attached to outer if statement
cout &laquo_space;nX &laquo_space;“is less than 10” &laquo_space;endl;

Question 11

What is an early return?

Answer 11

Using a return statement to end a function and return a value before all of its statements have been executed.

Question 12

When is a good time to use a switch statement?

Answer 12

When many else if statements are used; switch has better readability.

Question 13

Explain the flow of a switch statement.

Answer 13

The switch expression is evaluated to produce a value, and each case label is tested against this value for equality. If a case label matches, the statements after the case label are executed. If no case label matches the switch expression, the code under the default label is executed (if it exists).

Question 14

T/F: The expression of a switch statement must evaluate to an integral type (char, short, int, long, enum).

Answer 14

T; no floats or non-integers

Question 15

What is a constant expression?

Answer 15

An expression that evaluates to a literal, an enum, or a variable assigned a constant integral value.

Question 16

How is the constant expression given with a case executed?

Answer 16

If the case evaluation is equal to the switch evaluation

Question 17

What must be done if we do not want multiple cases to be executed?

Answer 17

A return, break, or goto statement must end the case.

Question 18

When is the ‘default’ keyword in a switch statement executed?

Answer 18

Only executed if no other case evaluates to true.

Question 19

What is “fall-through”?

Answer 19

When multiple cases are erroneously executed b/c they all evaluate to true and no return, break, or goto is present to prevent multiple case statements from executing.

Question 20

When a break statement is used, where does the program resume?

Answer 20

At the first statement following the end of the block.

Question 21

What is the proper syntax of a switch statement?

Answer 21

switch(evaluated_statement)
{
  case (value_possibility1):
     executed statements;
     break;
  case (value_possibility2):
      executed statements;
      break;
   .
   .
   .
   default:
        executed statements;
        break; OR exit(int code);
}

Question 22

What does a goto statement require, and what is its syntax?

Answer 22

A statement label, with the syntax:

myIdentifier:

Question 23

Given a statement label, what does a goto statement do?

Answer 23

Jumps to the statement label.

Question 24

What is one good use of a goto statement?

Answer 24

To check for correct input and keep prompting otherwise.

Question 25

T/F: The goto statement can jump anywhere, as long as a statement label is present.

Answer 25

F; The statement label must appear in the same function as the goto statement (function scope), and must not skip over any important declarations.

Question 26

What is the best practice regarding goto statements?

Answer 26

Avoid them unless necessary.

Question 27

What is the syntax of a while loop?

Answer 27

while (condition)
{
some code/iteration;
}

Question 28

What are the ways to break out of an infinite loop?

Answer 28

A return statement, a break statement, an exception being thrown, or the user killing the program.

Question 29

T/F: Iterator variables (aka loop variables) should be only 1 or two characters.

Answer 29

F; They should be specific to avoid ambiguities across programs.

Question 30

What is the syntax of a do loop?

Answer 30

do
{
mycode;
} while (condition);

Question 31

What is the syntax of a for loop?

Answer 31

for(Init statement; evaluation statement; iterator statement)
{
Iteration code;
}

Question 32

What is the scope of loop variables declared in a for loop?

Answer 32

Loop scope.

Question 33

T/F: Expressions cannot be omitted when writing a for loop.

Answer 33

F; Only the semicolons are required:

int iii=0; 
for ( ; iii < 10; )
 { 
    cout << iii << " ";    
    iii++; 
} 

This for loop produces the result:

0 1 2 3 4 5 6 7 8 9

Question 34

T/F: A for loop can have multiple declarations.

Answer 34

T;

for (int iii=0, jjj=9; iii < 10; iii++, jjj–)
cout &laquo_space;iii &laquo_space;” “ &laquo_space;jjj &laquo_space;endl;

Question 35

What is the difference between break and continue?

Answer 35

Break exits the loop entirely, whereas continue ends the current iteration (goes back to the top of the loop).

Question 36

What is a seed?

Answer 36

A starting number for a pseudo-random number generator (PRNG) which is transformed by the PRNG algorithm.

Question 37

What is the difference between srand() and rand(), and what is the name of the library in which they are included?

Answer 37

srand() should only be called once to set the initial seed value, and rand() generates the next random number in the sequence starting from the seed value set by srand()

Both are included in the cstdlib library.

Question 38

What is one way to convert the result of rand() to a random number in a given range?

Answer 38

rand() % (nHigh - nLow + 1)) + nLow;

Question 39

What is an example of a situation where you would WANT to set the seed and get reproducible results?

Answer 39

When testing a simulation; eliminate random element to fix other problems (i.e. debugging a random dungeon generator)

Question 40

How can time() be used to make an effective PRNG, and what library is it in?

Answer 40

Pass the value of the system clock, time(0), to srand():

using namespace std;

int main()
{

srand(time(0)); // set initial seed value to system clock
for (int nCount=0; nCount < 100; ++nCount)
{
    cout << rand() << "t";

    if ((nCount+1) % 5 == 0)
        cout << endl; } }

time() is included in the ‘ctime’ library.

Question 41

What are four qualities of a good PRNG, and does rand() exhibit these?

Answer 41

1) Distribution uniformity, or the quality of the PRNG generating any two numbers with equal probability.
2) Unpredictable/non-obvious sequence (the numbers generated after the initial seed value should not have an easily discernible pattern)
3) Dimensional distribution, or the equal probability of returning a low, mid, or high number
4) A long period (a PRNG should not repeat a value already returned for a very long time, because once it does, it will begin to repeat itself.

rand() is NOT a good PRNG, as it does not exhibit all of these properties.