1. RECURSION Recursion is a process where a function calls itself. main(){
printf(“RECURSION”);
main(); }
Recursive function can be effectively used to solve problems where solution is expressed in term of successively applying the same solution to subsets of the problem.

2. #include <stdio.h>
int factorial(int); //function prototype
main() {
int a;
printf("enter a num\n");
scanf("%d",&a);
int fact=factorial(a);
printf("The factorial of %d is: %d", a,fact);
getch(); }
int factorial(int a)
int fact;
if (a == 1)
return 1;
//recursive step of the factorial
else
fact= a*factorial(a-1); //calls the factorial function.
//The above calls the factorial function from within the factorial function.
return (fact);

3. File Management in C

4. Console oriented Input/Output
Console oriented – use terminal (keyboard/screen)
scanf(“%d”,&i) – read data from keyboard
printf(“%d”,i) – print data to monitor
Suitable for small volumes of data
Data lost when program terminated
Large data volumes
Need for flexible approach to store/retrieve data
Concept of files
File is a set of records/group of related data that can be accessed through the set of library functions.

5. Steps for file operation
Naming
Opening
Reading
Writing
Closing

6. File handling functions
FUNCTION NAME OPERATION
fopen() creats a new file for use
open an existing file for use
fclose() closes a file which has been opened for use
getc() reads a character from a file
putc() writes a character to a file
fprintf() writes a set of data values to a file
fscanf() reads a set of data values from a file
getw() reads an integer from a file
putw() writes an integer to a file
fseek() sets the position to a desired point in the file
ftell() gives the current position in the file
rewind() sets the position to the beginning of the file

7. Defining and opening file
Filename
Data structure
Data structure of a file is defined as FILE in the library of standard I/O function definition.
File should be declared as FILE before used.
3. Purpose
(e.g. reading, writing, appending)

8. General format for opening file
FILE *fp; /*variable fp is pointer to type FILE*/
fp = fopen(“filename”, “mode”);
Eg: FILE *p1,*p2;
p1=fopen(“data”,”r”);
p2=fopen(“result”,”w”);
Mode of files
r open the file for reading only
w open the file for writing only
a open the file for appending (adding) data to it

9. fopen() performs the following task:
Writing mode
if file already exists then contents are deleted,
else new file with specified name created
Appending mode
if file already exists then file opened with contents safe
else new file created
Reading mode
if file already exists then opened with contents safe
else error occurs.
Additional modes of operation
r the existing file is opened for both reading and writing w+ a+

10. Closing a file Syntax: fclose(file_pointer); Example: FILE *p1, *p2;
File must be closed as soon as all operations on it completed
Syntax: fclose(file_pointer);
Example:
FILE *p1, *p2;
p1 = fopen(“INPUT”, “r”);
p2 =fopen(“OUTPUT”, “w”);
……..
fclose(p1);
fclose(p2);

11. Input/Output operations on files
C provides several different functions for reading/writing
getc() – read a character
putc() – write a character
fprintf() – write set of data values
fscanf() – read set of data values
getw() – read integer
putw() – write integer

12. getc() and putc()
Handle one character at a time like getchar() and putchar()
syntax: putc(c,fp1);
c : a character variable
fp1 : pointer to file opened with mode w
syntax: c = getc(fp2);
fp2 : pointer to file opened with mode r
file pointer moves by one character position after every getc() and putc()
After entering the input data via keyboard, the program writes it character by
Character, to the given file. The end of the data is indicated by entering an EOF character, which is control-Z the file input is closed at this signal.

13. #include <stdio.h>
main() {
FILE *f1;
char c;
printf("DATA INPUT \n");
f1= fopen("INPUT", “w"); /* open file for writing */
while((c=getchar()) != EOF) /*get char from keyboard until CTL-Z*/
putc(c,f1); /*write a character to INPUT */
fclose(f1); /* close INPUT */
printf("DATA OUTPUT \n");
f1=fopen("INPUT", "r"); /* reopen file */
while((c=getc(f1))!=EOF) /*read character from file INPUT*/
printf("%c", c); /* print character to screen */
fclose(f1);
getch();
} /*end main */