- Goal of computer programming:
- We write a computer program to solve a problem or perform a task
- In order to solve a problem,
we need:
- An algorithm
(detailed steps that solve the problem)
- Information !!!
The basic fact of life is that without information, we cannot complete the task !!!
- An algorithm
(detailed steps that solve the problem)
- Example: compute the sum of
2 numbers
- Algorithm:
perform an addition
- Information: the value of the 2 numbers
Without the value of the 2 numbers, we cannot perform the addition operation !!!
- Algorithm:
perform an addition
- A computer program consists of:
- computer instructions that
tells a computer precisely
what to do to accomplish the job
- (Lots of) information to guide the algorithm to do the job
- computer instructions that
tells a computer precisely
what to do to accomplish the job
- This fact is expressed in the
title
of a classical Computer Science book:
- The title of this
classical Computer Science book
reflects the fact that to
solve a problem (write a program)
with a computer, you need:
- An algorithm, and
- Information (that is stored in data structure)
- Statements:
- Statement =
an instruction written in a
(High level) Programming Language
- A statement tells a computer in very precise terms what exactly it must do
Example of statements:
- Store the value 26 in the memory cell named "A"
- Add the number A to the number B
- If the number A ≥ 0 then do this otherwise do that
- Statement =
an instruction written in a
(High level) Programming Language
- Variables:
- A variable
= a
identifiable memory cell
stores
information that is
necessary to
solve a problem
- A variable behaves like a
piece of paper that is
identified
by a unique name
where we can
record (a small amount of) information
Example:
- A variable behaves like a
piece of paper that is
identified
by a unique name
where we can
record (a small amount of) information
- A variable
= a
identifiable memory cell
stores
information that is
necessary to
solve a problem
- Data structure:
- A data structure = a collection of variables that store related information
Example:
- One variable stores the name of a person
- Another variable stores
the phone number of
a same person
- These 2 variables together would form a data structure
- Previously discussed:
- There are different kinds
of information
E.g.: gender information, marital status information, etc
- Each kind of
information uses its own
information encoding method
Example:
- Gender information: 0 = male and 1 = female
- Marital status information: 0 = single, 1 = married, and so on...
- There are different kinds
of information
- Information is stored in
variables.
- Consequently,
there are different types
of variables:
- Numerical variables, that
are used to store data such as:
age, salary, and so on.
- Textual variables, that are
used to store
alpha-numerical data such as
text in books, news paper articles,
webpages, and so on.
- Boolean (logical) variables, that are
used to store the
logical value
TRUE
and FALSE
- Etc.
- Numerical variables, that
are used to store data such as:
age, salary, and so on.
- Fact:
- Different types of variables use different encoding methods to represent/encode the information
- Data type:
- Data type =
all the values that use the
same encoding method
In other words:
- One data type uses one (same) encoding method (to represent the same kind of information)
- Data type =
all the values that use the
same encoding method
- A programming language
always provides a number of
built-in data types
to get your started
Common built-in data types:
- Single precision
floating point numbers
- Double precision
floating point numbers
- Integer numbers
- A character type
- A logical data type
The built-in data types are called primitive data types
- Single precision
floating point numbers
- In addition, a
modern programming language
allows the programmer to
define his/her own data types
These are called user-defined types.
- Recall:
- A variable is
a storage location for
information (data)
- It is like a (small) piece of paper
where you can write a number
You can also erase an esisting number and write a new number on the paper (= variable).
- A variable is
a storage location for
information (data)
- A variable in a program
is created by a
- Variable definition clause
- In modern programming languages,
we must "define" every
variable in the computer program
- Effect of a variable definition:
- Some memory cells will be
reserved to store the
information
- Each variable definition must use a unique name to identify the variable.
- So: a variable definition clause will
tell the computer to
create the variable
that will be identified
by that (unique) name
This is like telling the computer to:
- get a new sheet of paper and
- tag the new sheet of paper with the name of the variable
- Some memory cells will be
reserved to store the
information