Chpater 3

Outline The definition of Syntax The Definition of Semantic Most Common Methods of Describing Syntax

Introduction We usually break down the problem of defining a programming language into two parts. Defining the PL’s syntax Defining the PL’s semantics In other words, In Order to understand any Programming Language, you need to understand: Syntax Semantics – What is the Syntax & the Semantics?

What is the Syntax & the Semantics?  Syntax:  It is the Form of the its (expressions, statement, program unit.  Semantic:  It the meaning of those (expressions, statements, Program units) The boundary between the two is not always clear.

Syntax It is the Form of the its (expressions, statement, program unit. A sentence is a string of characters over some alphabet. A language is a set of sentences. A lexeme is the lowest level syntactic unit of a language (e.g., *, sum, begin). A token is a category of lexemes (e.g., identifier).

Syntax Ex: While ( Boolean Exprission ) Statement While ( x <10 ) { cout<< x << endl ; }

Formal Methods of Describing Syntax 1.Backus-Naur Form and Context-Free Grammar 2.Extended BNF

Formal Methods of Describing Syntax Context-Free Grammars – Developed by Noam Chomsky in the mid-1950s – Language generators, meant to describe the syntax of natural languages Backus Normal Form (BNF) – Invented by John Backus to describe Algol 58 – BNF is equivalent to context-free grammars

Review What is the Syntax? What is Semantic? Give an example of a syntax? How can we describe the syntax? What is a language? What is a statement? What is a token? What is a lexmes?

C++ Traning Do you want to know how to Program? If yes, what do you need to write your first Program in C++? 1.Install the Visual Studio.NET on your computer. 2.Knowing the basics of C++. What are the basics of C++? – We will study most of the basics in the class step by step.

C++ Traning The Basic Structure of C++ Code: – Library: #include – Using the namespace using namespace std; – The function main int main() { } – Your code cout<<“hello”;

C++ Write a program that would print the phrase I am studying Programmig Languages in this summer 1.Library 2.Using namesapce 3.The function main 4.Your code

The Solution #include Using namespace std; int main( ) { cout<<“I am studying Programming Languages this summer”; }

C++ Variables: a variable is a storage location and an associated symbolic name (an identifier) which contains some known or unknown quantity or information Types: 1.int 2.char 3.double 4.Float How to define a variable in C++? [Type] [variable name] = [value] ; int x = 10; [Type] [variable name]; int z;

Question Write a program that will calculate the area of the rectangle where its tall = 10 and width = 3 and show the result?

The Solution #include Using namespace std; int main( ) { int tall = 10; int width= 3; int area ; area = tall * width ; cout<<“Area = ” << area ; return 0; }