# Lesson #6. Loops. Simple tasks

Дата изменения: 6 октября 2020

## Theory

Lection # 6 in pdf format

• Loops are used to repeat actions
• The loop consists of: a loop header and a loop body
• One loop iteration is one repetition of the loop body
• The simpliest type of loops is loop.
Syntax:

loop n do
some operator;


### For loop

• For loop is a loop with a counter
• After each iteration counter increments by 1

### While and Repeat loop

Syntax of While loop:

while condition do
statements


Syntax of Repeat loop:

repeat
statements
until condition


### Loops

Lab 1:

To do: Print digit 1 ten times.

The resulting example:

1 1 1 1 1 1 1 1 1 1


✍ Algorithm:

begin loop 10 do print(1); end.

Note: Since this moment you should implement protection against invalid input with Assert function.
{0.3 points} Task 1, loop:
To do: An integer A (A > 0) is given. Output the word «Hello» A times. You need to put commas between the words.

Note: You should check if the number is positive:

assert(a>0,'a bad input; the variable a must be > 0');

The resulting example:

'Please enter how many times: A ='
>>> 3
Hello, Hello, Hello


[Program name: task-01-loop.pas]

{0.3 points} Task 2, loop:
To do: Two integers K and N (N > 0) are given. Output the number K N times (loop must be used)

Note: You should check if input numbers are positive (assert()).

The resulting example:

'enter the number to output:  K= '
>>> 4
'enter how many times to output: N= '
>>> 3
4 4 4


[Program name: task-02-loop.pas]

Lab 2:

To do: Print numbers from 1 to 10.

The resulting example:

1 2 3 4 5 6 7 8 9 10


✍ Algorithm:

{0.4 points} Task 3, loop:
To do: An integer A (A > 0) is given. Output integers between 0 and A (including the value of A) in ascending order and output the number (quantity) of these numbers.

The resulting example:

'Enter a number where to stop: A= '
>>> 5
0 1 2 3 4 5  quantity = 6
---
'Enter a number where to stop: A= '
>>> 3
0 1 2 3 quantity = 4


[Program name: task-03-loop.pas]

Lab 3:

To do: Print numbers from 10 downto 1.

The resulting example:

10 9 8 7 6 5 4 3 2 1


✍ Algorithm:

{0.4 points} Task 4, loop:
To do: An integer A (A > 0) is given. Output integers between A and 0 (including the value of A) in discending order.

The resulting example:

'Enter a number to begin the output:'
>>> 5
result: 5 4 3 2 1 0
---
'Enter a number to begin the output:'
>>> 3
result: 3 2 1 0


[Program name: task-04-loop.pas]

Lab 4:

To do: Print a power of 2 starting at 0; eight powers (1 2 4 8 … 128).

The resulting example:

1 2 4 8 16 32 64 128


✍ Algorithm:

{0.5 points} Task 5, loop:

To do: An integer A (A > 0) is given. Print 3^A (3 in a power of A). You should use multiplication (*). It is forbidden to use standard functions.

Note: You should use the writelnFormat function:

WritelnFormat('3 in the power of {0} = {1}', a, ?);

The resulting example:

'Enter a number - power of 3: A= '
>>> 4
3 in the power of 4 = 81
---
'Enter a number - power of 3: A= '
>>> 2
3 in the power of 2 = 9


[Program name: task-05-loop.pas]

### For loops

Lab 5:

To do: Print a sequence of numbers from 1 to 10.

The resulting example:

1 2 3 4 5 6 7 8 9 10


✍ Algorithm:

{0.3 points} Task 1, for loop:

To do: Two integers K and N (N > 0) are given. The number K must be printed N times.

Note: to check if N > 0 you should use assert function:

assert(n > 0, 'bad input, n must be > 0');

The resulting example:

'enter the number to output, please: K ='
>>> 4
'enter how many times to output: N ='
>>> 3
4 4 4


[Program name: task-01-for.pas]

{0.4 points} Task 2, for loop:

To do: Two integers A and B are given (A < B). Output integers between A and B (including the values of A and B themselves) in ascending order and output the number (quantity) of these numbers. You should use assert function too.

The resulting example:

'enter two numbers, please: A= , B ='
>>> 0  >>> 5
0 1 2 3 4 5  quantity = 6
----
'enter two numbers, please:  A= , B ='
>>> 2  >>> 7
2 3 4 5 6 7 quantity = 6


[Program name: task-02-for.pas]

Lab:

To do: Output the numbers from 10 downto 1 (10 9 8 7 6 5 4 3 2 1).

✍ Algorithm:

 begin for var i:=10 downto 1 do begin print(i) end; end.

{0.4 points} Task 3, for loop:

To do: Two integers A and B are given (A < B). Output integers between values of A and B (including A and B themselves) in discending order.

The resulting example:

'enter two numbers, please: A= , B ='
>>> 5  >>> -2
5 4 3 2 1 0 -1 -2


[Program name: task-03-for.pas]

### While and Repeat loops

Lab 6:

To do: Print a sequence of numbers: 0 1 2 3 4.

The resulting example:

0 1 2 3 4


✍ Algorithm:

{0.2 points} Task 1, while & repeat loop:

To do: Output the sequence 15 16 17 18 19 20 … 30 (from 15 to 30). Make it twice: with while loop and with repeat loop.

Note: you should use different variables for loops counters.

The resulting example:

results with while loop:
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
results with repeat loop:
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30


[Program name: task-01-while-repeat.pas]

{0.2 points} Task 2, while & repeat loop:

To do: Output the sequence of integers: 3 5 7 9 … 21 (from 3 to 21 with a step = 2). Make it twice: with while loop and with repeat loop.

[Program name: task-02-while-repeat.pas]

{0.2 points} Task 3, while & repeat loop:

To do: Output the sequence of integers: 20 18 16 … 2 (from 20 downto 2 with a step = 2). Make it twice: with while loop and with repeat loop.

[Program name: task-03-while-repeat.pas]

{0.2 points} Task 4, while & repeat loop:

To do: Output the sequence of integers: 15 12 9 6 3 0 (from 15 downto 0 with a step = 3). Make it twice: with while loop and with repeat loop.

[Program name: task-04-while-repeat.pas]

{0.2 points} Task 5, while & repeat loop:

To do: Output the sequence of real numbers: 0.1   0.3  0.5   0.7  0.9   1.1. Make it twice: with while loop and with repeat loop.

[Program name: task-05-while-repeat.pas]

{0.2 points} Task 6, while & repeat loop:

To do: Output the sequence of real numbers: 0.0   0.5  1.0   1.5  2.0   2.5. Make it twice: with while loop and repeat loop.

[Program name: task-06-while-repeat.pas]

{0.3 points} Task 7, while & repeat loop:

To do: Two integers A and B are given (A < B). Output integers between A and B (including A and B themselves) in ascending order and output the number (quantity) of these numbers. Make it twice: with while loop and repeat loop.

The resulting example:

'enter two numbers, please: A= , B ='
>>> -1  >>> 5
results with a while loop:
-1 0 1 2 3 4 5  quantity = 6
results with a repat loop:
-1 0 1 2 3 4 5  quantity = 6


[Program name: task-07-while-repeat.pas]

{0.5 points} * Task 8, while loop:

To do: Positive integers N and K are given. Using only the operations of addition and subtraction, find the quotient of dividing N by K, as well as the remainder of this division.

Note 1. Use friendly variable names for quotient and remainder. For example: quotient is quotient, remainder is remainder. Possibly: quot / rem.

Note 2. Don’t forget to implement protection against invalid input with Assert.

The resulting example:

'N = '
>>> 12
'K = '
>>> 4
quotient = 3, remainder = 0
---
'N = '
>>> 27
'K = '
>>> 5
quotient = 5, remainder = 2


[Program name: Extask-08-while.pas]

{0.5 points} * Task 9, while loop:

To do: Positive numbers A and B (A >= B) are given. The segment of length A contains the maximum possible number of segments of length B (without overlays). Without using the multiplication (*) and division(/, div) operations, find the length of the unoccupied part of segment A.

Note 1. To specify that input values are not valid, add Assert operators to the program. They must be placed after the data is entered, but before the calculations begin. Check how Assert works on incorrect input data:

Assert((A > 0) and (B > 0));
Assert(A >= B);


The resulting example:

A =
>>> 10
B =
>>> 4
result: 2
---
A =
>>> 12
B =
>>> 4
result: 0


[Program name: Extask-09-while.pas]

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