1. Introduction to Programming Lecture 6

2. Functions – Call by value – Call by reference Today's Lecture Includes

3. Functions

4. Laboratory Stool

5. Constructing a laboratory Stool

6. Task: Making a stool – Subtask: Make a seat Make legs for the stool Assemble them

7. What are functions? How are they defined ? How are they declared ? What values are passed to functions ? What values do functions return ? What we will study today …

8. Function Function name { Body of the function }

9. Function Two types of functions: 1.Functions that return a value 2.Functions that do not return a value

10. return-value-type function-name( argument-list ) { declarations and statements } Function

11. return-value-type function-name( argument--type-list) ; main ( ) { : } Declaration of Function

12. Example int function-name ( int, int, double ) ; void main ( ) { …. }

13. int function-name ( int i, double j ) { … } Definition of Function

14. int square ( int ) ; Return Type of Function int square ( int i ) { return ( i * i ) ; } Declaration Definition

15. int x ; x = square ( i ) ; Function Call

16. double raiseToPow ( double x, int power ) { double result ; int i ; result = 1.0 ; for ( i = 1 ; i <= power ; i ++ ) // braces first { result * = x ; // result = result *x } return ( result ) ; } Example: Function to calculate integer power ( X n )

17. include void main ( ) { double x ; int i ; cout << “ Please enter the number “ ; cin >> x ; cout << “ Please enter the integer power that you want this number raised to “ ; cin >> i ; cout << x << “ raise to power “ << i << “is equal to “ << raiseToPow ( x, i ) ; } Code to Call the raisetopow Function

18. Call By Value

19. Calling function Called function

20. Area of the Ring ____ Area of Inner Circle Area of Outer Circle = Area of the Ring

21. double circleArea ( double radius ) { return ( 3.1415926 * radius * radius ) ; } Example: Function to calculate the area of a circle

22. main ( ) { : ringArea = ( 3.1415926 * rad1 * rad1 ) – ( 3.1415926 * rad2 * rad2 ) ; } Calculating ringArea without using Function

23. Exercises 1.Modify the raise to power function so that it can handle negative power of x, zero and positive power of x. 2.For the area of ring function put in error checking mechanism.

24. We used functions for breaking complex problems into smaller pieces, which is a top-down structured approach. Each function should be a small module, self contained and it should solve a well defined problem. Variable names and function names should be self explanatory. Always comment your code What we have studied so far?

25. #include Header Files

26. int functionName ( int, int ); Prototype Return value Assignment List with data type

27. double pi = 3.1415926; Using Header Files It is better to define this value in a header file It is better to define this value in a header file Then simply by including the header file in the program this value is defined and it has a meaningful name Then simply by including the header file in the program this value is defined and it has a meaningful name

28. #define pi 3.1415926 Name can be used inside a program exactly like a variable It cannot be used as a variable CircleArea = pi * radius * radius Circumference = 2 * pi * radius #define

29. Identifier is any name user creates in his/her program Functions are also identifiers Labels are also identifiers Scope of Identifiers

30. Scope means visibility A variable declared inside a block has visibility within that block only Variables defined within the function has a scope that is function wide Scope of Identifiers

31. Example void functionName ( ) { int i ; } ….. }

32. Do not create variables with same name inside blocks, inside functions or inside bigger blocks Try to use separate variable names to avoid confusion Reuse of variables is valid Identifiers Important Points

33. # include int i ; File Scope Global variable

34. Can be used anywhere in program Can cause logical problems if same variable name is used in local variable declarations For good programming Try to minimize the use of global variables Try to use local variables as far as possible Global Variable

35. Global Scope Anything identified or declared outside of any function is visible to all functions in that file Function level scope Declaring variables inside a function can be used in the whole function Block level scope Variables or integers declared inside block are used inside block Visibility of Identifiers

36. for ( int i = 0 ; i < 10 ; i++ ) It is block level scope declared in for loop When for is finished “ i ” no longer exists Example: Block Scope

37. #include int i ; void f ( void ) ; main ( ) { i = 10 ; cout<< “ within main i = “ << i ; f ( ) ; } Example: Global Scope

38. void f ( void ) { cout<< “ Inside function f, i =“ << i ; i = 20 ; } Example: Global Scope

39. #include int f ( int ) ; main ( ) { int i = 10 ; cout << “In main i = " << i ; f ( i ) ; cout << " Back in main, i = " << i ; } Example: Call by Value s

40. int f ( int i ) { cout << "In function f, i = " << i ; i *= 2 ; cout << "In function f, i is now = “ << i ; return i ; } Example: Call by Value

41. double square ( double x ) { return x * x ; } main ( ) { double number = 123.456 ; cout << “ The square of “ << number << “ is “<< square ( number ) ; cout << “ The current value of “ << number << “is “ << number ; } Example : Square of a Number

42. #include double sqrt ( double ); log 10, pow ( x y ), sin, cos, tan … Math.h

43. Today we studied Functions Variable Scope