Introduction to computer science course Fall-2018

1. +
Dr Ramadan Babers
Faculty of Science - Helwan University
Fall-2018
Introduction
to
Computer
LEC - 7

2. +
Introduction to
Programming
Languages
2

3. Chapter 1 Outlines
 Introduction
 Different ways that people use computers.
 How a Program Works
 Compilers and Interpreters
 Ambiguity
 Grammar
 Derivation
3

4. 1. Introduction
4
Different ways that people use computers.
In school,
Students use computers
for tasks such as
 writing papers,
 searching for articles,
 sending email, and
 participating in online
classes.

5. 1. Introduction (Cont.)
5
Different ways that people use computers.
At work,
People use computers to
 analyze data,
 make presentations,
 conduct business
transactions,
 communicate with
customers,
 control machines and
 do many other things.

6. 1. Introduction (Cont.)
6
Different ways that people use computers.
At home,
People use computers for
tasks such as
 paying bills,
 shopping online,
 communicating with
friends and family, and
 playing computer
games.

7. 1. Introduction (Cont.)
7
Computers can do such a wide variety of
things because they can be programmed.
This means that computers are not designed
to do just one job, but to do any job that their
programs tell them to do.
A program is a set of instructions that a
computer follows to perform a task

8. 2. How a Program Works
8
CONCEPT:
 A computer’s CPU can
only understand
instructions that are
written in machine
language.
 Because people find it
very difficult to write entire
programs in machine
language, other
programming languages
have been invented.

9. 2. How a Program Works (Cont.)
9
 CPU only understands
machine language, it is
difficult for people to
write programs in
machine language.
 For this reason,
assembly language was
created as an alternative
to machine language.

10. 2. How a Program Works (Cont.)
10
 Assembly language programs cannot be executed
by the CPU, however.
 The CPU only understands machine language, so a
special program known as an assembler is used to
translate an assembly language program to a
machine language program.

11. 3. Compilers and Interpreters
11
 Because the CPU understands only machine
language instructions, programs that are written in
a high-level language must be translated into
machine language.
 Depending on the language that a program has
been written in, the programmer will use either a
compiler or an interpreter to make the translation.

12. 12
 Many languages require
you to compile (translate)
your program into a form
that the machine
understands.
 Python is instead directly
interpreted into machine
instructions.
compile execute
outputsource code
Hello.java
byte code
Hello.class
interpret
outputsource code
Hello.py
3. Compilers and Interpreters (Cont.)

13. 3.1 Compiler
13

14. 3.2 Interpreters
14
The Python language uses an interpreter, which is a program that both
translates and executes the instructions in a high-level language
program. As the interpreter reads each individual instruction in the
program, it converts it to machine language instructions and then
immediately executes them.

15. 4. Ambiguity
15
 Why Do We Need
Programming
Language
 Can we use natural
languages like
English?

16. 4. Ambiguity (Quiz)
16
 Would you rather be paid $100 weekly or
biweekly?
o Prefer to be paid $100 weekly.
o Prefer to be paid $100 biweekly.
o It depends.
o Prefer not to be paid at all.

17. 4. Ambiguity (Quiz)
17

18. 4. Ambiguity (Quiz)
18
 Would you rather be paid $100 weekly or
biweekly?
o Prefer to be paid $100 weekly.
o Prefer to be paid $100 biweekly.
o It depends.
o Prefer not to be paid at all.
Different people understand different ways

19. 5. Grammar
19
Noun example: I / Python
Verb example: eat / like
Noun Verb
Sentence Subject Verb Object
Noun Noun

20. 6. Derivation
20
Sentence Subject Verb Object
Subject
Object
Verb
Verb
Noun
Noun
Noun
Noun
like
eat
I
Python
Non-terminal
terminal
Noun cookies

21. 6. Derivation (Cont.)
21
Sentence Subject Verb Object
Non-terminal
terminal
Noun
like Noun
Verb
I
Object
Python
Subject
Object
Verb
Verb
Noun
Noun
Noun
Noun
like
eat
I
Python
Derivation:
Starting from some non-terminals,
follow the roles to derive the
sequence of terminals

22. 6. Derivation (Quiz)
22
Sentence Subject Verb Object
Which of these sentences can be produced from
the following grammar? Starting from Sentence
o Python eat cookies
o Python eat Python
o I like eat
o Eat python cookies