1. Backus Naur form

2. Different Programming Languages
Different programming languages take different forms
For i = 1 to 10 (is VB6)
For(i=1, i<=10, 1++) (is C++)
A Visual Basic compiler would not understand the C++ syntax.

3. BNF
We need a set of rules that specifies every part of the language to overcome this problem
We use Backus Naur Form or Syntax Diagrams

4. BNF Example All languages use integers
The integer can be a single digit
<integer>::= <digit>
This is read as an integer is defined (::=) to be a digit
Now we define the digit
<digit>::=1|2|3|4|5|6|7|8|9
Anything that needs defining is put in <>

5. BNF Example Our full definition is <integer>::= <digit>
We need to consider the length of the integer
All integers more than one digit begin with digit
<integer>::= <digit> <integer>
This definition is recursive (calls itself)

6. BNF Example

7. BNF Example
<unsigned integer>::=<digit>|<digit><integer>
This can be expressed through a syntax diagram
All definitions should be created by paths through the diagram from left to right

8. BNF Example

9. A Signed Integer - BNF Example

10. BNF Example