Introduction to Programming Languages

1. Introduction to Programming Languages Programming in C

2. Programming Languages • The need for Programming Languages • Programming Languages allow programmers • to express computations that are to be carried • out by computers

3. Programming Languages • The need for Programming Languages • Machine level Programming Languages are • understood by machines, but are difficult for • humans to understand and express ideas High Level Programming Languages

4. Programming Languages • High Level Programming Languages: • Abstract out the underlying complexities of • computer by providing a view of the • computer that provides a higher level of • abstraction

5. Programming Languages • Programming Languages are defined by: Syntax rules Semantics rules

6. Syntax • The rules describing the forms of Programming Languages constructs • Describes which sequence of characters are valid programs of the language

7. Semantics • The rules describing the meaning of syntactically correct programs • Describes what will the program do if executed

8. Lexical Rules • Describe the valid words (lexems) from which a valid program can be constructed • Constants 9, 9.6, 1.7E+3, 'b' • Identifiers book, salary • Reserved (key) words if, return, do

9. Syntax Rules • Describe which sequence of lexems form valid programs • Assignment is Identifier = Expression • Expression is Identifier or Constant • ratio = 0.9 Color = red (valid) • name = John Smith Ratio = 0.0.9 (invalid)

10. Semantic rules • Describe consistency rules. • A variable must be declared before it is used. • Describe the meaning of valid programs. Count = 9; Value of the variable Count becomes 9 Count = Count + 1; Value of the variable Count is incremented by 1

11. Compiler Compiler Program in a high level language Equivalent program in the machine language

12. Elements of Programming Languages • Variables • Variable Types • Operators • Expressions • Assignment • Control Structures • Functions • etc.

13. Variables • Abstraction of Computer Memory. Name A variable has a name

14. Variable • Variable Type: Abstraction of the set of values the variable may assume: • Integer (int) 9, 7, -12990 • Character (char) 'A', '\n', 'b' • Boolean True, False • WeekDay Monday, Wednesday

15. Operators • Arithmetic Operators + , - , * , / , ... • Relational Operators < , <= , == , !=... • Logical Operators && , || , !

16. Operators • Precedence rules: Define the order by which the operators are evaluated. • Associativity rules: Define the order by which the operators having the same precedence are evaluated.

17. Expressions • Arithmetic Expressions: • Operands: variables constants • Operators: + - * / ... • Example: 3+5*7 3*(a+b)/n

18. Expressions • Relational Expressions: • Operands: variables constants • Operators: > >= < <= == != ... • Example: 3 > 5 a+b <= 3*x

19. Expressions • Boolean Expressions: • Operands: Boolean variables Boolean constants: True, False • Operators: and - && or - || not - ! • Example: a && b ((a+b) >= 12 ) && (x != y)

20. A Assignment • Changes the value of a variable. <Assignment> ==> <Var> = <Expression> • Example: A = 5; 5

21. Control Structures • Describe the order of statement execution • Sequence • Selection • Iteration

22. Control Structures • Sequence Statement-1; Statement-2; . . . Statement-n; Statements are executed sequentially one after another.

23. Expr is evaluated. If the result is True, statements of Sequence-1 will be executed. Expr is evaluated. If the result is True, statements of Sequence-1 will be executed. Otherwise, statements of Sequence-2 will be executed. Control Structures • Selection: if ( Expr ) { Sequence-1 } if (Expr) { Sequence-1 } else { Sequence-2 }

24. Control Structures • Iteration: while (Expr) { Sequence-1 } Expr is evaluated. If the result is True, Statements of Sequence-1 will be executed. Expr is evaluated again. If the result is True, Statements of Sequence-1 will be executed. ...