Chapter 4

Question 1

Explain the While Loop

Answer 1

Format:
while (condition)
{
statement A; // runs while the condition is true until condition is no longer true (called an iteration)
}
statement B; // the statement that is run once the condition is false

Question 2

Explain the Do-While Loop.

Answer 2

Format:
do
{
statements;
}
while (condition);

Unlike while loops, do-while loops check the condition at the end and decide whether or not to repeat the loop.

Question 3

Explain the For Loop

Answer 3

Format:
for (initialization; condition; update;)
{
statements;
}

Executes the initialization, loops through the code as long as the condition is true, and performs the update after each loop

For loops are great for when you want your loop to repeat a set amount of times.

Question 4

What is a local variable?

Answer 4

A local variable is any variable declared inside of a loop. They only exist inside of that loop and cannot be accessed outside of the loop.

Question 5

What is a global variable?

Answer 5

A global variable are variables that can be accessed anywhere in the entire program.

Question 6

When should you use a while loop?

Answer 6

You should use a while loop when you know your loop isn’t going to run a fixed number of times or if the stopping condition is more complicated than a simple comparison.

Note: loops are interchangeable to accomplish the same purpose, however some loops are easier to use.

Question 7

When should you use a do-while loop?

Answer 7

You should use a do-while loop when your loop needs to run at least once.

Question 8

When should you use a for loop?

Answer 8

You should use a for loop when you know ahead of time that your loop will run a fixed number of times

Question 9

In a for loop, what is the difference between i = 0 vs i = 1?

Answer 9

i = 0 means it starts at 0, while i = 1 means it starts at 1. This will affect your output which is why sometimes people may run into an off by one error.

Question 10

What is a nested loop?

Answer 10

A nested loop is one loop inside of another.

Ex:
int i = 1, j;
while (i <= 3)
{
j = 1;
while (j <= i)
{
cout &laquo_space;i &laquo_space;”,” &laquo_space;j &laquo_space;“ - ”;
j++; }
i++;
cout &laquo_space;endl;
}

*An example of what a nested loop may be used for is creating rows and columns (i = the row, j = column)

Question 11

What is the purpose of a break statement?

Answer 11

A break statement is used to break out of the loop

Note: a break statement cannot be used to break out of multiple nested loops. It only jumps out of the inner loop.

Question 12

What is the purpose of the continue statement?

Answer 12

A continue statement is used to skip the remaining part of the loop and continues to the next iteration.

Question 13

What is the <random> library used for in C++ ?</random>

Answer 13

The <random> library in C++ allows us to use a random number generator</random>

Question 14

What is rand() and what is its function?

Answer 14

• rand() is used to generate random integers
• it generates a random integer between 0 and RAND_MAX

Question 15

What library do you need to include to use RAND_MAX?

Answer 15

include <cstdlib></cstdlib>

Question 16

What is RAND_MAX?

Answer 16

RAND_MAX generates the largest integer that rand() can generate.

EX: random integer between [0, RAND_MAX]
- int r = rand();

EX: random integer between [0, 10]
- int r = rand () % 11; // rmb position starts at 0 so using the number 11 gives us [0, 10].

EX: random integer in the range [a, b]
- int r = a + rand() % (b - a + 1);
// we use b - a + 1 because we are not sure if a starts at 0 as it could be any number.

Question 17

What are pseudorandom number generators?

Answer 17

Pseudorandom numbers are not completely random. They are initialized using an argument passed seed. We can call srand ()

Question 18

How do you generate different sequences of random numbers?

Answer 18

You use a different seed at each run time!

Question 18

What library is used to define time (nullptr) and what is its function?

Answer 18

<ctime> is used to define time (nullptr) and gives an unsigned integer based on system time.
</ctime>

Question 19

How do you generate a different seed at each run time?

Answer 19

srand(static_cast<int> (time (nullptr) ) );</int>

When different seeds are provided, different random sequences are generated

Question 20

What is a sentinel value?

Answer 20

A sentinel value indicates the end of a data set, but is not part of the data.

Ex:
cout &laquo_space;“Enter values, Q to quit: “; bool done = false;
while (!done)
{
cin&raquo_space; value;
if (cin.fail())
{ done = true; } else
{ //Process value… }
}

The program will only exit the loop if cin receives a fail input (in this example a failed input would be anything besides Q)

Question 21

Write a program that computes the sum.

Answer 21

double total = 0;
double input;
while ( cin&raquo_space; input )
{
total = total + input;
}

*Keep a running total: a variable to which you add each input
value.
* Initialize total with 0
* While-loop is terminated if input is not a valid number
* (cin&raquo_space; input) returns a bool value to its caller: true (successful reading) or false (failure reading)

Question 22

Write a program that computes the average.

Answer 22

double total = 0; int count = 0; double input;
while (cin&raquo_space; input) {
total = total + input;
count++;
}
double average = 0;
if ( count > 0 ) { average = total / count; }

*Keep a total and a count of all values
*Initialize total and count with 0
*Count how many numbers with variable count

Question 23

Write a program to find the minimum or maximum.

Answer 23

double largest;
cin&raquo_space; largest;
double input;
while (cin&raquo_space; input)
{
if (input > largest)
{
largest = input;
}
}
cout &laquo_space;”Largest number is ” &laquo_space;largest &laquo_space;endl;

*To find the largest (smallest) value, update the largest (smallest)
value seen so far whenever you see a larger (smaller) one.

Question 24

Write a program to count the number of inputs that match a target value.

Answer 24

double target = 100, input;
int count = 0;
while (cin&raquo_space; input)
{
if (input == target)
{ count++;}
}
cout &laquo_space;“The number of matches is ” &laquo_space;count;

*Increase count only if a match is found
*Count how many matches with variable count (Use count++)

Question 25

Write a program that compares adjacent values. Suppose you wantt o check whether a sequence contains adjacent duplicates such as 1 7 2 9 9 4 9 Q. What’s the output if input is 1 7 7 7 2 2 9 Q?

Answer 25

double input, previous;
cin&raquo_space; previous;
while ( cin&raquo_space; input )
{
if (input == previous)
{
cout &laquo_space;“Duplicate neighbors”
&laquo_space;endl;
}
previous = input;
}

*To compare adjacent inputs, store the preceding input in a variable
*If the input is 1 7 7 7 2 2 9 Q, the code will print Duplicate neighbors three times.