Programming Languages

1
Programming Languages

• An interesting history of software can be found
  on
• History of Computing Software Index

2
From Algorithm to Program

• A program is an algorithm
• As seen in the lecture on algorithms, a program
  is a very precise algorithm that is written in
  primitives
• We know that programs have several levels the
  lowest being machine code.

3
Generations of Languages

• Machine Language, 1st generation
• Assembler, 2nd generation
• High level languages, 3rd generation

4
1st Generation Programming Language was Machine
code

• Suppose you were given the following list of
  instructions to perform
• 0001 0011 0011 1011
• 1101 0111 0001 1001
• 1111 0001 1101 1111
• 0000 1100 0101 1101
• 0001 0011 0011 1011
• it is extremely confusing for a computer
  programmer

5
2nd Generation Programming language was Assembler
language

• Program from the Virginia Tech Courseware
• LOAD   5
• STORE  15
• EQUAL  15
• JUMP   6
• HALT
• ADD    1
• JUMP   3

6
2nd Generation Programming languages were machine
oriented

• op-codes are given an English mnemonic (memory
  aid)
• Second thing, not shown in courseware is
  symbolic addressing

7
2nd generation programming languages were machine
oriented.

• In order to write a program the programmer had to
  have a basic understanding of the machine to use
  instructions such as load, store, etc.
• Must understand that math can only be done in the
  ALU

8
The 3rd Generation programming languages started
with FORTRAN

• FORTRAN was invented in the early 1950s and was a
  scientific language
• FORTRAN Stood for FORmula TRANslation
• Developed by a team headed by John Backus
• In the 1950s most computers were used for
  scientific purpose since they were too expensive
  for businesses

9
Example of a FORTRAN program

• Remember our Assembler language program
• LOAD   2
• STORE  13
• LOAD   5
• STORE  14
• LOAD   13
• ADD    14
• STORE  15
• HALT

10
In FORTRAN this program would be

• x 2
• y 5
• Z x y
• Note that the programmer does not have to know
  about load and store operations etc.

11
First business language was COBOL Common Business
Oriented Language

• Was developed by the US Department of Defense and
  first version was around 1960
• Rear Admiral Dr. Grace Murray Hopper was the
  project leader
• Why did the military need a business language?

12
COBOL Why the military?

• Who has one the biggest payrolls to pay?
• Who purchases millions of of equipment?
• Who has one of the biggest inventories?

13
COBOL

• Since business computing is more data processing
  oriented relater than calculation oriented the
  language is very poor at formulas but can define
  data in many different ways.
• The language uses English like statements to
  define the program.
• The example that we had in FORTRAN would be
  written Add X to Y giving Z.

14
Newer languages

• Programming languages have come a long way since
  the 1960s. Today you would possible use Java,
  Visual Basic. C, etc.
• There are hundreds of programming languages
  available today. An interesting list of languages
  can be found on the following hyperlink The
  Programming Languages Index

15
Five basic concepts of a 3rd generation
Programming language

• variables
• expressions
• control structures
• input/output
• abstraction

16
Identifiers Constants and Variables

• Identifiers are descriptive names that are mapped
  to locations in the computer's memory (RAM
  location)
• Once a memory locals has a name it is easier to
  locate (do not have to remember the RAM address)
• There are two types of Identifiers, they are,
  Variables and constants

17
Variables

• a named memory location
• value can change while a program is running
• allows data to be stored in computer memory

18
Constant

• a named value
• value always remains the same while a program is
  running
• allows programs to be easily modified

19
Assigment

• C and Java
• PriceOfShoes 19.95
• Pascal
• TAXRATE 0.045

20
Expression

• result 6 10 / 2 - 4 2
• Order of operations
• result (6 10) / 2 - 4 2

21
Control Structures

• Sequence
• Selection (If and Else)
• Loop
• Subprograms

22
Input/output

• two types of I/O
• User I/O is interactive since this type of input
  is generally accomplished via the keyboard or
  mouse and a monitor.
• File I/O allows us to store data in a file on the
  computer and then read the data from this file

23
Now go to the courseware using the below
hyperlink and review the topic

• Online CS Modules Programming Languages