Functions in C can be defined by the user or come from standard libraries. User-defined functions must be declared with a name, return type, and parameters. Functions are called by passing actual arguments which are assigned to formal parameters. Arguments can be passed by value, where copies are used, or by reference, where the function accesses the original variables. Recursion is when a function calls itself, reducing the problem size each time until a base case is reached.

1. Presentation on function in 'c-language' by- Sanju & Amit

2. function Defination:- function is a self-contained block of program that performs a coherent task of some kinds. Function is also called as modular programming.

3. Types of function Library function

4. User define function

5. library function Library function are nothing but commonly required function together and stored in library. The library function are not required to be written by us. Printf( )

6. Scanf( )

7. User define function Main ( ) This function as to be developed by the user at the time of writing a program. ‘ main’ is specially used function in C. Every program must have main function to indicate, where the program begins its execution.

8. Things to make function Function prototype Function call

9. Function definition

10. Function call A function call is an expression containing a simple type name and a parenthesized argument list. The argument list can contain any number of expressions separated by commas. It can also be empty. For example: res= sum ( a , b); prime(&no);

11. Function definition In C user- written functions should normally be declared prior to its use to allow compiler to perform type checking on arguments used in its call statement. Syntex- Return_data_type function_name (data_type Var_name, …..);

12. Function name: this is the name given to the function. int sum (int a, int b) Note- “ sum ” is the function name Return data type: this specifies the type of data given back to the calling construct. int sum (int a, int b) Note- “ int ” is the return data type

13. Passing parameters : this specifies the data type of each variables, the values of which are expected to be transmitted to the function. These variables are known as formal parameters. int sum ( int a , int b ) Note- “ int a , int b ” are the parameters.

14. Function declaration and prototypes All identifiers in C need to be declared before they are used. For functions the declaration needs to be before the first call of the function. A full declaration includes the return type and the number and type of the arguments. This is also called the function prototype. The prototype gives a lot of information about the function. #include <stdio.h> int sum (int a, int b); //prototype it tells it the return type.

15. it tells it how many parameters there are.

16. Argument – passing of values b/w the main program and the function takes place through arguments. Formal and actual argument- The actual arguments are the arguments with which the function can be called. Simply function call contains actual arguments. // Call func with actual arguments i and j. func( i, j ); -The formal arguments are the arguments with which the function can be defined. function defination contains formal arguments void Func( int i ); // Function prototype … Func( 7 ); // Execute function call

17. CALL BY VALUE AND CALL BY REFERENCE Call by value- Whenever we called a function and passed something to it we have always passed the ‘values’ of variables to the called function. Such function calls are called ‘calls by value. in this context we are working on copies of actual argument.

18. swap ( a, b ) ; main( ) { int a = 10, b = 20 ; printf ( &quot;\n a = %d b = %d&quot;, a, b ) ; }

19. swap ( int x, int y )

20. {

21. int t ;

22. t = x ;

23. x = y ;

24. y = t ;

25. printf ( &quot;\n x = %d y = %d&quot;, x, y ) ;

26. }

27. The output of the above program would be:

28. x = 20 y = 10

29. Call by refrence- An argument passing convention where the address of an argument variable is passed to a function or procedure as opposed to passing the value of the argument expression.

30. Int sum(int *,int *); void main() { int i=10, j=20; K=sum(&i,&j); Printf(“%d”,k); } Int sum(int *a, int *b) { int c; C=*a+*b; return( c ); }

31. Recursion A function is called recursive if a statement with in the body of the function calls the same function. Sometimes called circular definition. Recursion is thus the process of defining something in terms of itself.

32. Main() { int a, fact; printf(“\n enter any number”); Scanf(“%d”, &a); fact = rec (a); Printf(“factorial value=%d”,fact); } int rec (int x) { int f ; if (x==1) return(1); else f=x*rec(x-1); return (f); }

33. Need for implementing recursion- Decomposition into smaller problems of same size. Recursive call must diminish problem size.

34. Advantages It reduces the Complexity in a program by reducing the code.

35. It also reduces the Time to run a program. In other way,Its directly proportional to Complexity.

36. Its easy to find-out the errors due to the blocks made as function definition outside the main function.

37. Return statement The return statement terminates the execution of a function and returns control to the calling function. Execution resumes in the calling function at the point immediately following the call. r eturn expression ; return; The default return type is int.

38. Thank you