C2110 UNIX and programming Lesson 5 / Module 2 -1C2110
UNIX and programming
Petr Kulhanek
kulhanek@chemi.muni.cz
National Center for Biomolecular Research, Faculty of Science
Masaryk University, Kamenice 5, CZ-62500 Brno
PS / 2020 Distance form of teaching: Rev1
Lesson 5 / Module 2
C2110 UNIX and programming Lesson 5 / Module 2 -2Basics
of Programming
https://cs.wikipedia.org/wiki/Algoritmus
C2110 UNIX and programming Lesson 5 / Module 2 -3-
Algorithmization
Problem formulation
Problem analysis
Creating an algorithm
Build the program
Program testing
Problem formulation
It is necessary to precisely formulate the requirements, determine
the initial data, the required results and the accuracy of the
solution (for numerical problems).
Problem analysis
We will verify that the task is solvable for the expected input data
and, depending on the nature of the task, we will suggest the most
suitable solution.
Creating an algorithm
We will design a clear sequence of operations that need to be
performed in order to correctly solve the task.
Build the program
Based on the algorithm, we will create the source code of the
program in a selected programming language.
Program testing
Finding syntax errors in the source code and logical errors in our
own design. Verification of the program's functionality on the
entered data.
C2110 UNIX and programming Lesson 5 / Module 2 -4-
Algorithm
Algorithm is a precise guide or procedure by which a given type of task can be solved. The
concept of an algorithm most often appears in programming, where it means a theoretical
principle of problem solving (as opposed to the exact notation in a particular programming
language). In general, however, the algorithm can occur in any other scientific field.
Required features:
▪ Determinability - the algorithm must be accurate, comprehensible and unambiguous,
i.e. the next step is clearly defined at each point and must always provide the same
results for the same input data. (The operation of the algorithm must not depend on
the will of the person or on the characteristics of the devices that run it).
▪ Generality - the algorithm is not used to solve only one task, but it is a solution of a
whole group of tasks, which differ from each other only by input data. Input data may
vary within certain limits.
▪ Finality - we must obtain the searched results after a finite number of steps, the
algorithm must end after a finite number of steps.
Writing algorithms:
▪ verbally
▪ pseudocode
▪ graphically (flow chart, etc.)
C2110 UNIX and programming Lesson 5 / Module 2 -5-
Flowchart
processing block
input/output block
Yes
No
decision block
junction (start, end)
The marks are combined so that the
diagram describes a clear sequence of
operations that must be performed in order
for the task to be solved correctly. The
operations or groups of operations to be
performed are entered into the individual
marks.
A flowchart is a graphical representation of an algorithm. The diagram consists of marks
(blocks) that are executed in order from the beginning to the end of the diagram in the
direction of the arrows.
There are also other marks that we will not
use yet.
C2110 UNIX and programming Lesson 5 / Module 2 -6-
Examples
I < N
Yes
No
write "X"
I= 0
N = 10
S
E
write "\n"
I= I + 1
Flowchart: Word description:
1. Insert value 0 into variable I.
2. Insert value 10 into variable N.
3. Is the value of variable I less than N?
YES - continue with point 4
NO - continue with point 7
4. Print the X character.
5. Increase the value of variable I by one.
6. Continue with point 3.
7. Print the end of the line.
8. End
C2110 UNIX and programming Lesson 5 / Module 2 -7-
Examples
I < N
Yes
No
write "X"
I= 0
N = 10
E
write "\n"
I= I + 1
Algorithm Bash Script
#!/bin/bash
I=0
N=10
while [ $I -lt $N ]; do
echo –n "X"
((I=I+1))
done
echo ""
Result:
$ ./my_script
XXXXXXXXXX
$
S
C2110 UNIX and programming Lesson 5 / Module 2 -8Data
Structures
Data structures are used to store data. The basic data structures include:
a) variable
b) field
c) record
d) object
Variable is a named location in memory that contains a value. Each variable is of defined
type which restricts possible operations with the variable. The type of a variable can be
specified when creating the variable (explicit type) or it can be specified only when using
the variable (implicit type). Variable type affects how data is stored in computer memory.
Examples:
A=“test value"
B=5
C=10.458
D=B+C
E=A+B
text (string)
integer
real number (floating point number)
C2110 UNIX and programming Lesson 5 / Module 2 -9-
Operations
Basic operations:
= assignment
+ addition
- subtraction
* multiplication
/ division
Logical operations:
== equal
!= not equal
< smaller than
<= less than or equal
> larger than
>= greater than or equal
processing block
decision block
I= 0
N = 10
I= I + 1
F=10*X*X+5*X+1
F=(X+2)*(Y-6)+3
I != N I < N I < N+5
C2110 UNIX and programming Lesson 5 / Module 2 -10-
Input
Program input can be information entered by user from the terminal or can be redirected
from a file, or from another program using a pipe.
Basic operations (pseudocode):
read var load a value into a variable var
write "Enter value:"
read A
Example:
Program writes a query to the user and
expects input, which is loaded into the
variable A after entering it by the user.
The input defined in this way reflects the basic possibilities of the bash language. I do not
recommend using other input options at this stage.
C2110 UNIX and programming Lesson 5 / Module 2 -11-
Output
Output is the terminal. The terminal behaves like a printer in which a character that has
already been printed cannot be taken back. In addition, the printer can go to the beginning
of a new line by typing a \n character into the terminal.
Basic operations (pseudocode):
writestr "string” prints characters (string) stated in quotation marks
writevar var prints the value of the variable var
writestr “Entered value: "
writevar A
writestr "\n"
Example:
Prints the text "Entered value:" followed by
the value of variable A. The cursor will move
to a new line.
The output defined in this way reflects the basic possibilities of the bash language. I do not
recommend using other output options at this stage.
C2110 UNIX and programming Lesson 5 / Module 2 -12-
Homework
➢ Algorithmization
C2110 UNIX and programming Lesson 5 / Module 2 -13Homework
- Instructions
1. Create a flowchart for one from the following assignments. In the flowcharts, use only
the marks and operations, including I/O, that are listed in this presentation.
2. Draw the flowcharts in an appropriate software:
▪ e.g., program dia which is available on the WOLF cluster (or you can install it on a
VM with Ubuntu: $ sudo apt-get install dia)
3. Insert the resulting diagrams into the Homework vault Algorithm in pdf format. The file
name will be in the following format:
SurnameL05X.pdf
where X is the chosen task. Files that are named differently will not be checked
(automatic name changes made by IS are allowed).
4. Deadline for submission is January 24, 2021 11:59 PM.
Recommendation: For cycles, place the decision block before the processing block.
C2110 UNIX and programming Lesson 5 / Module 2 -14Task
A
In the form of a flowchart, describe an algorithm that writes a square of X characters to a
device of terminal type (printer). Side length of the square is entered by the user.
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
X X X X X X X X X X
C2110 UNIX and programming Lesson 5 / Module 2 -15Task
B
In the form of a flowchart, describe an algorithm that writes a right triangle with
characters to the output device of the terminal type (printer) X, so that one perpendicular
is located at the top and the other on the left. The length of the perpendicular is entered
by the user.
X X X X X X X X X X
X X X X X X X X X
X X X X X X X X
X X X X X X X
X X X X X X
X X X X X
X X X X
X X X
X X
X
C2110 UNIX and programming Lesson 5 / Module 2 -16Task
C
In the form of a flowchart, describe the algorithm that writes a right triangle with
characters to the output device of the terminal type (printer) X, so that one perpendicular
is located at the bottom and the other on the left. The length of the perpendicular is
entered by the user.
X
X X
X X X
X X X X
X X X X X
X X X X X X
X X X X X X X
X X X X X X X X
X X X X X X X X X
X X X X X X X X X X