Programming Fundamentals
Lecture 01 – Introduction to Programming
Edirlei Soares de Lima
<edirlei.lima@universidadeeuropeia.pt>
Computer Programs
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Programs are created to solve problems and perform specific
tasks.
Problem: your car has a flat tire… What you do? What are the
steps to replace the car’s tire?
Computer Programs
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Problem: your car has a flat tire… What you do? What are the
steps to replace the flat tire?
Textual solution:
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“Open the trunk and make sure that all the equipment is there. If not,
close the trunk and ask for a ride. If so, remove the reflective triangle,
position it about 30 m from the car. Then, get the new tire and the
jack. Place the jack and lift the car ...”
Computer Programs
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Problem: your car has a flat tire… What you do? What are the
steps to replace the flat tire?
Graphical solution:
Computer Programs
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Problem: your car has a flat tire… What you do? What are the
steps to replace the flat tire?
Algorithmic solution:
open(trunk)
if equipment_is_there == FALSE then
close(trunk)
ask_for_ride()
else
get(triangle_sign, trunk)
place(triangle_sign, car_position - 30)
get(jack, trunk)
get(new_tire, trunk)
...
Machine Code
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A computer's central processing unit (CPU) only runs machine
code.
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Machine code is a strictly numerical language and is intended to run as
fast as possible.
The instructions causes the CPU to perform specific task, such
arithmetic operations and registry manipulations.
Machine code is represented by sequences of binary digits.
Exemple:
Adding the registers 1 and 2
and placing the result in
register 6.
Jumping to the address 1024
High-Level Programming Languages
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While it is possible to write programs directly in machine
code, it is very complex to manage individual bits and
calculate numerical addresses manually.
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Today, the vast majority of programs are written in high-level
programming languages.
In a high-level language, instead of dealing with registers and
memory addresses, programmers manipulate variables,
functions, loops, boolean expressions, arrays, etc.
Popular Programming Languages
Example of Code in Lua
local cels
local fahr
io.write("Temperature in Celsius: ")
cels = io.read()
fahr = 1.8 * cels + 32
io.write("Temperature in Fahrenheit: ", fahr, "\n")
Compilation Process
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Programs written in high-level languages cannot be directly
executed in the CPU.
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Before running the code, it must be translated to machine code.
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This task (compilation) is performed by a program called
compiler.
Examples of compiled languages:
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C, C++, Basic, Pascal, …
Interpreted Programming Languages
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Not all programming languages are compiled. Some of them
are interpreted.
An interpreted language uses an interpreter program to
execute the code directly, translating each statement into a
sequence of one or more operations that are performed by
the interpreter.
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Examples of interpreted languages:
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Lua, Java, JavaScript, Python, PHP, …
Development Cycle (Compiled)
Program
Text Editor
Code
Development
Compiler
Compilation
Program
Output
Test
Development Cycle (Interpreted)
Program
Text Editor
Code
Development
Interpreter
Output
Test
Algorithms
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What is an algorithm?
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A detailed sequence of actions to perform in order to accomplish a
task or solve a problem.
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It is an unambiguous specification of how to solve a class of problems.
Is independent of programming language.
Even simple tasks can be described by sequences of actions:
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Example: Add two numbers
1
2
3
) Write the first number in
rectangle A.
) Write the second number in
rectangle B.
) Add the number of rectangle A
with the number of rectangle B
and put the result in rectangle C.
A
B
C
Algorithms: Example 1
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Algorithm: calling a friend on the telephone
Input: the telephone number of your friend
Output: none
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Steps:
1
2
3
4
5
6
7
. Pick up the phone and listen for a dial tone;
. Press each digit of the phone number on the phone;
. If busy, hang up the phone, wait 5 minutes, jump to step 1;
. If no one answers, leave a message then hang up;
. If no answering machine, hang up and wait 2 hours, then jump to step 1;
. Talk to friend;
. Hang up the phone;
Exercise 1
1
) Write an algorithm for an everyday task. Pick a common or
interesting task and breaking it down to the level that a
computer might understand.
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Some suggestions: brushing your teeth, taking a shower, a cooking
recipe, how to get to the university, …
Make it extra specific: pretend you are explaining to someone with no
common sense and no knowledge of the task, like an alien or a robot.
Format: follow the same format of the example 1 and specify what is
the input (like ingredients in a recipe) and the output (if needed).
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Try to use conditions by using words such as “if”, “else” or “otherwise”.
Try to use repetitions by using the word such as “jump to step” when
the same step must be repeated.