Textbook Solutions To Exercises Chapter 6: Repetition - Section 6.6

Textbook Solutions to Exercises Chapter 6: Repetition - Section 6.6 Textbook Solutions to Exercises 1 - 10 Chapter 6: Repetition - Section 6.6 1.

Write a program containing an infinite loop which outputs the series of integers starting at 5 and going up by 5s. Revise this program to output the integers starting at 5 and decreasing by 10s. SOLUTION: Write a program containing an infinite loop which outputs the series of integers, starting at 5 and going up by 5s.

% The "06-01a Solution” Program var count : int := 5 loop put count count:= count + 5 end loop Revise this program to output the integers starting at 5 and decreasing by 10s.

% The "06-01 b Solution" Program var count: int := 5 loop put count count := count - 10 end loop

Textbook Solutions to Exercises Chapter 6: Repetition - Section 6.6 6-2.

Write a program that endlessly tells you to "Have a good day". Try stopping execution. Change it so that it is a program to wish you a good day only six times. SOLUTION: Write a program that endlessly tells you to "Have a good day".

% The "06-02a Solution” Program loop put "Have a nice day" end loop Change it so that it is a program to wish you a good day only six times.

% The "06-02b Solution” Program for i: 1 .. 6 put "Have a nice day" end for 6-3.

Write a program that reads words entered one to a line and counts how many words have been entered before you give the signal word "end" to stop execution of the program. Experiment to determine what happens if you put several words on a line as you enter them. SOLUTION:

% The "06-03 Solution” Program var word: string var count: int := 0 loop put "Enter a word:".. get word exit when word = "end" count := count+ 1 end loop put count," words were read before 'end'." If more than one word is entered on a line, each one is read in turn as though it were entered properly when the prompt is given. However, the count is increased by only one because we are pssing through the loop only once.

Textbook Solutions to Exercises Chapter 6: Repetition - Section 6.6 6-4.

A series of marks is to be entered and averaged. Before you enter the series, you are to have the program ask you how many marks there are in the series then read it in. Test your program to see that it works for series of different lengths, say four marks or six marks. SOLUTION:

% The "06-04 Solution” Program var numberOfMarks, mark: int var sum : int := 0 assert may be new to you. You can put "How many marks are there:" .. probably see what it does, but check get numberOfMarks what Turing’s Help says at Help, Turing Reference, Search, assert. assert numberOfMarks > 0 for i: 1 .. numberOfMarks put "Enter a mark:" .. Here we use a variable holding input from the user get mark as the number of passes sum := sum + mark through a counted loop. end for put "The average mark is ", sum / numberOfMarks: 4 : 1

Textbook Solutions to Exercises Chapter 6: Repetition - Section 6.6 6-5.

Write a program that announces at each repetition of a loop the number of times it has executed the loop. Have it stop at each execution with the message Type

'more'

to

continue

A sample Execution window might be Loop execution number Type 'more' to continue more Loop execution number 2 Type 'more' to continue more Loop execution number 3 Type 'more' to continue stop

1

SOLUTION:

% The "06-05 Solution” Program var count: int := 0 loop count := count+ 1 put "Loop execution number", count put "Type 'more' to continue" var ans: string get ans exit when ans not= "more" end loop

To make the program pause, simply ask for input from the user.

Textbook Solutions to Exercises Chapter 6: Repetition - Section 6.6 6-6.a

Write a program to output a table of values of the integers starting at 1 and their squares. Label the table at the top of the columns. For example, your output might look like this Number 1 2 3 4 5

Square 1 4 9 16 25

Try to format the output so that it looks attractive. What happens as the numbers get larger and larger? Change the program to output the first 100 integers rather than attempting to go on forever. SOLUTION:

% The "06-06a1 Solution” Program put "Number Square" var val :int := 1 loop put val: 3, val** 2: 8 val := val + 1 end loop

Formatting is done with spaces for first line of output (the titles) and fields for the numbers. Experiment to make it look right.

As the numbers get larger, the number of digits in the SOLUTION increase. However, Turing has an upper limit on integer values and this limit is passed the program halts with an error message. This implementation of Turing limits integers to 2**31-1 (a number slightly over 2 billion).

% The '06-06a2 Solution” Program put "Number Square” for val: 1 .. 100 put val: 3, val** 2 :8 end for

Textbook Solutions to Exercises Chapter 6: Repetition - Section 6.6 6-6.b Modify your program so that in one for loop you output the following Num 1 2

Square 1 4

Num 21 22

Square 441 484

Num 41 42

Square 1681 1764

Num 61 62

Square 3721 3864

1600

60

3600

80

6400

Continue through to 20

400

40

SOLUTION:

% The "06-06b Solution” Program put "Num Square Num Square Num Square Num for val: 1 .. 20 put val: 3, val** 2 : 7, val + 20 : 7, (val+ 20)

Square" ** 2 : 7,

val + 4 0 : 7 , (val+40)** 2 : 7, val + 60 :7, (val+60)** 2 :7

end for

6-7.

Write a program using a loop counting backwards. Output the index of the loop on each execution so the output is the same as the count down for a rocket launch. Arrange the output so that it is all on one line like this 5

4

3

2

1

SOLUTION:

% The "06-07 Solution” Program for decreasing countdown : 5 .. 1 put countdown : 2 .. end for

Remember, the index of a counted loop can be used for output.

Textbook Solutions to Exercises Chapter 6: Repetition - Section 6.6 6-8.

Write a program to output a backwards count by 5s from 100 down to 5. Modify it so that you count from 100 down to 50. Modify it so that before you start the count you can input a number between 100 and 50 so that the program will stop when the count would be less than the number input. For example the execution might be like this: What number do I stop at? 82 Stop when count less than 82 100 95 90 85 SOLUTION: Write a program to output a backwards count by 5s from 100 down to 5.

% The "06-08a Solution" Program const startValue := 100 const minStopValue := 5 const decrement := 5 var counter: int := startValue var stopValue : int := minStopValue loop exit when counter < stopValue put counter: 3 counter := counter - decrement end loop Modify it so that you count from 100 down to 50.

% The "06-08b Solution" Program const startValue := 100 const minStopValue := 50 const decrement := 5 var counter: int := startValue var stopValue : int := minStopValue loop exit when counter < stopValue put counter: 3 counter := counter - decrement end loop

Textbook Solutions to Exercises Chapter 6: Repetition - Section 6.6 Modify it so that before you start the count you can input a number between 100 and 50 so that the program will stop when the count would be less than the number input.

% The "06-08c Solution" Program const startValue := 100 const minStopValue := 50 const decrement := 5 var counter: int := startValue var stopValue : int := minStopValue put "What number do I stop at? ".. get stopValue put "Stop when count less than ", stopValue assert stopValue <= startValue and stopValue >= minStopValue loop exit when counter < stopValue put counter: 3 counter := counter- decrement end loop

6-9.

Write a program to find the sum of a number of terms of the infinite series 1 + x + x**2 + x**3 + x**4 + ... where the number of terms n to be evaluated and the value of x are input before the summation begins. Experiment with different values of n and x. SOLUTION:

% The "06-09 Solution" Program var n: int put "How many terms should be evaluated:".. get n var x: real put "Enter a value for x:" .. get x Starting to count with 0 solves a tricky var sum : real := 0 problem that you might have run into when for term : 0 .. n- 1 you tried this exercise. Why is it used here? sum := sum + x ** term end for put "Sum of terms is:", sum Aside: if x is between 0 and 1, this series sums to l/(l-x) in the limit.

Textbook Solutions to Exercises Chapter 6: Repetition - Section 6.6 6-10. Write a program to compute the bank balance at the end of each year for 10 years resulting from an initial deposit of $1000 and an annual interest rate of 6%. Output for each year end the number of the year, the initial balance, the interest for the year, and the balance at the end of the year. SOLUTION:

% The "06-10 Solution" Program const numberOfYears := 10 const interestRate := .06 const initialDeposit := 1000.00 var balance : real := initialDeposit put "Year Start Balance Interest End Balance " for year: 1 .. numberOfYears const interest := balance * interestRate put year: 3, balance: 15 : 2, interest: 10 : 2, balance + interest: 13 :, 2 balance := balance + interest end for