Problem Solving and 'C' Programming

Transcription

1 Problem Solving and 'C' Programming Targeted at: Entry Level Trainees Session 09: Functions 2007, Cognizant Technology Solutions. All Rights Reserved. The information contained herein is subject to change without notice. C3: Protected

2 About the Author Created By: Jeyshankar Perumal (125623) Credential Information: Version and Date: Technical Skills: UNIX/C/C++/Oracle Experience: 8.5 Years PSC/PPT/1107/1.0 2

3 Icons Used Questions Tools Hands on Exercise Coding Standards Test Your Understanding Reference Try it Out A Welcome Break Contacts 3

4 Problem Solving and 'C' Programming Session 09: Overview Introduction: This session introduces the concept of functions, explains its significance and also how functions can be defined and used in C. 4

5 Problem Solving and 'C' Programming Session 09: Objective Objective: After completing this session you will be able to:» Define functions» Pass arguments to function» Implement recursive functions» Pass arrays in a function 5

6 Introduction Functions are smaller self-contained components which carry out some specific, well defined task. Benefits:» It facilitates top-down modular programming» It avoids the need for redundant code» It facilitates reusability» It can be used to build a customized library of frequently used routines 6

7 Need for Functions As real world applications become more complex and large, several problems arise. Most common are:» Algorithms for solving more complex problems become more difficult and hence difficult to design.» Algorithm s implementation becomes more difficult because of the size of the program.» As programs become larger, testing, debugging and maintenance will be a difficult task. So complex problems can be modularized and can be implemented by using user defined functions 7

8 Function Prototypes Declaration of a function is called function Prototype. Prototype specifies the signature of the function, the return type and number and data types of the arguments. Functions must be declared before it is called. In C, prototyping is not mandatory, it is needed if a function call precedes function definition. 8

9 Function Prototypes (Contd.) Example:» int find_big(int,int); Function find_big returns integer value, takes 2 integer arguments» void swap(int *,int *); Function swap does not return any value, takes 2 pointer variables.» float add(float, int); Function add returns float value, takes 1 float variable and 1 integer variable. 9

10 Function Definition Used to define the function with appropriate name, parameters, and the task to be carried out by the function. Can be defined at any location in the program. A function definition has two principle components: Function header (first line) and Function body. 10

11 Function Definition (Contd.) Syntax: return-type fn-name(type arg1, type arg2, ) { } local variables declaration; executable statement 1; executable statement 2; : return expression; 11

12 Function Definition (Contd.) Function header:» Function-name specifies the name of the function and it must be a valid identifier.» arg1, arg2 are called formal arguments.» Return-type represents the type of the data item returned by the function. 12

13 Function Definition (Contd.) Function body:» Function can have declaration statements and any number of valid executable statements.» return statement is used to transfer the control back to the calling program Syntax: return; or return(expr);» expr can be a variable name, constant value, or any single valued expression. 13

14 Function Call Functions can be invoked by specifying its name, followed by a list of parameters enclosed within parentheses. Syntax: [vble name =] fn-name(actual arguments); 14

15 Recursion If a function is having a self-reference, it is called recursion. It is a process by which a function calls itself A recursive function must have the following properties:» The problem must be written in a recursive form» There must be a base criteria (terminating condition) for which the function doesn t call itself. 15

16 Recursion: Example Example: Program to find the factorial of a given number. main() { int n; long fact(int); printf( Enter an integer\n ); scanf( %d,&n); printf( Factorial = %ld,fact(n)); } long fact(int k) { if (k<=1) return 1; else return(k*fact(k-1); } 16

17 Nesting of Functions Functions may be nested to any level. The main function may call another function, which in turn can call another function, which may include again a function call. Example: void fun1() { fun2(); } void fun2() { fun3(); } 17

18 Passing Arguments A function is referenced by using its name and providing appropriate values for the arguments. Functions may be classified as:» Functions with no arguments and no return value» Functions with no arguments but return value» Functions with arguments but no return value» Functions with arguments and return value 18

19 Passing Arguments to a Function There are two approaches to pass the information to a function via arguments They are:» Call by Value» Call by Reference 19

20 Call by Value The values of the actual arguments are copied in to the respective formal arguments. Actual and Formal parameter refers to the different memory locations and only the value of actual argument is copied into the formal argument. The value of the actual argument will remain same. 20

21 Call by Reference The addresses of actual arguments are passed to the formal arguments. Formal arguments refer to the same memory location of actual arguments. Formal arguments should be a pointer variable or array. 21

22 Function and Arrays To pass an array to a function, it is enough to give the name of the array as argument. Array name will be interpreted as base address of the array and that address will be given to the formal parameter. Formal parameter can be an array or pointer which points an array. 22

23 Function and Arrays (Contd.) Example: int maximum(int val[]) /*size of the array need not be mentioned.*/ { : } main() { : for( i = 0; i < 5; ++i ) scanf("%d", &values[i] ); max = maximum(values); /*array name is used to pass an entire array without any subscripts*/ : } 23

24 Passing Multidimensional Arrays Example: void print_table(int xsize,int ysize, float table[][5]) { int x,y; for (x=0;x<xsize;x++) { for (y=0;y<ysize;y++) printf("\t%f",table[x][y]); printf("\n"); } } Note: Second dimension is mentioned with its size. In case of three dimensional arrays second and third dimension has to be mentioned. This is to represent the column size. 24

25 Q & A Allow time for questions from participants 25

26 Try it Out - 1 Problem Statement: Write a program to find a factorial of a given number 26

27 Try it Out - 1 (Contd.) Code: #include <stdio.h> main() { int number; prompt(); /*function call no parameters */ scanf( "%d", &number ); } factor(number); /* function call with parameters */ getchar(); getchar(); prompt() /* function */ { printf("input a number... "); } Refer File Name : <ses9_1.c> for soft copy of the code 27

28 Try it Out - 1 (Contd.) Code: factor(int t) /* function */ { long sum = 1; int i ; } for (i = 1 ; i <= t ; i++) sum = sum*i; printf("factorial %d is %ld\n", t, sum); Refer File Name : <ses9_1.c> for soft copy of the code 28

29 Try it Out - 1 (Contd.) How it Works: This program calls a function which prompts the user to enter a number for which we need to find factorial. Then calls another function factor() with the given number as argument. The factor() function finds the factorial of the given number and prints on the screen. 29

30 Q & A Allow time for questions from participants 30

31 Test Your Understanding 1. State whether the following statements are True or False: a. C functions can return only one value under their function name. b. A function can be defined and placed before the main function. c. The return type of a function is float by default. d. Program execution always begins in the main function irrespective of its location in the program. 31

32 Test Your Understanding (Contd.) 2. What will be the output of the following code? int dim(int arr[]) { return (sizeof(arr)/sizeof(int)); } void main() { int a[10]; printf("%d", dim(a)); } 32

33 Practice Exercise 1. Write a program to find the Standard Deviation (SD). Use functions to find out mean, square, summation, SD. 2. Write a program to convert the given decimal number to binary using recursive function. 33

34 Problem Solving and 'C' Programming Session 09: Summary Functions are smaller self-contained components which carry out some specific, well defined task. Functions facilitates reusability and brings logical clarity to our programs. C functions should be considered with three aspects: i. Function definition ii. Function call iii. Function prototyping Arguments can be passed to a function via call by reference method or by call by value method. 34

35 Problem Solving and 'C' Programming Session 09: Summary (Contd.) Arrays can be passed to a function by simply specifying its name. A function calling itself is called recursion. 35

36 Problem Solving and 'C' Programming Session 09: Source C Reference Card (ANSI) C Reference Manual by Dennis Ritchie Programming in C: A Tutorial by Brian W. Kernighan, Bell Laboratories Byron Gottfried, Programming in C, Tata McGraw Hill Deitel & Deitel, C How to Program, Third Edition, Prentice Hall Disclaimer: Parts of the content of this course is based on the materials available from the Web sites and books listed above. The materials that can be accessed from linked sites are not maintained by Cognizant Academy and we are not responsible for the contents thereof. All trademarks, service marks, and trade names in this course are the marks of the respective owner(s). 36

37 You have completed the Session 09 of Problem Solving and 'C' Programming 2007, Cognizant Technology Solutions. All Rights Reserved. The information contained herein is subject to change without notice.