1. C Input / Output Prabhat Kumar Padhy1 1

2. C Input / Output? C only has no provision for I/O.
char name[5][100];
C Input / Output?
C only has no provision for I/O.
Then printf and scanf possess what ?
So these functions are actually are standard library funcions and there are many as well.
The numerous library functions available for I/O can be classified into as the below.
Console I/O functions
Disk I/O functions
Port I/O functions

3. Console Input and Output Functions
Formatted Functions
Unformatted Functions
Type
Input
Output
Char
Scanf()
Printf()
Int
Float
String
Type
Input
Output
Char
getch()
getche()
getchar()
fgetchar()
putch()
putchar()
Int
Float
String
gets()
puts()

4. C Format Specifiers Datatype Specifier Integer short signed
char name[5][100];
C Format Specifiers
Datatype
Specifier
Integer
short signed
short unsigned
long signed
long unsigned
unsigned hexadecimal
unsigned octal %d %u
%ld
%lu %x %o
Float double %f
%lf
Signed char
Unsigned char %c
String %s

5. C Input / Output? main() { main() printf(“\n %f%f%f”,5.0,13.5,133.9);
int weight=63;
printf(“\n weight is %d kg”,weight);
printf(“\n weight is %2d kg”,weight);
printf(“\n weight is %4d kg”,weight);
printf(“\n weight is %6d kg”,weight);
printf(“\n weight is %-6d kg”,weight); }
main() {
printf(“\n %f%f%f”,5.0,13.5,133.9);
printf(“\n %f%f%f”,305.0,1200.9,3005.3); }
printf(“\n %10.1f%0.1f%0.1f”,5.0,13.5,133.9);
printf(“\n %0.1f%0.1f%0.1f”,305.0,1200.9,3005.3);
char str1[] = “IIIT”;
char str2[] = “Sricity”;
char str3[] = “Delhi”
printf(“\n %20sf%20sf”,str1,str2);
printf(“\n %20sf%20sf”,str1,str3);

6. C Format Specifiers Esc Seq Purpose \n New line \t Tab \b Backspace \r
char name[5][100];
C Format Specifiers
main() {
char ch=‘a’;
int i=125;
float a = 12.44;
char s[] = “hello world”;
printf(\n%c%d%f”,ch,ch,ch);
printf(\n%s%d%f”,s,s,s);
printf(\n%c%d%f”,i,i,i);
printf(\n%f%d\n”,a,a); }
Esc Seq
Purpose \n
New line \t
Tab \b
Backspace \r
Carriage return \f
Form feed \a
Alert \’
Single Quote \”
Double quote \\
Backslash

7. sprintf() and sscanf()
char name[5][100];
sprintf() and sscanf()
main() {
char ch=‘A’;
int i=12;
float a = 3.14;
char str[30];
printf(\n%d%c%f”,i,ch,a);
sprintf(str,”%d%c%f”,i,ch,a);
printf(\n”%s”,str); }
Printf prints on the console, where as sprintf() stores them in a string
Sscanf(), is counter part of sprintf(). It allows us to read characters from a string and to convert and store them in C variables according to specifiers
It is a good tool for doing in-memory conversions of characters.

8. Example Program: sprintf, sscanf
printf("\n\n Your name ( Format - Without MiddleName) : %s %s",firstname,lastname);
    //printing extracted firstname and lastname
   printf("\n\n____________________________________________________________________");
    printf("\n\n Enter Date of Birth (Format : dd/mm/yyyy e.g. 21/09/2002) : ");
    gets(bdate); //reading birth-date in string format
    sscanf(bdate,"%2d/%2d/%4d",&day,&month,&year);
    //reading data from bdate string and extracting to individual int variables day,month & year
    
printf("\n\n Date of Birth (Format - YYYY-MM-DD) : %d-%d-%d",year,month,day);
    //self-explained - see output
printf("\n\n Date of Birth (Format - MM-DD-YYYY) : %d-%d-%d",month,day,year);
     printf("\n\n");
    return 0; }
/*C Program#134 - sscanf() & sprintf() functions in C.
1. sscanf() reads characters from an array & stores them in different arguments.
2. sprintf() prints data items in the form of characters into an array.
#include<stdio.h>
int main() {
    char fullname[60],shortname[30],firstname[20],middlename[20],lastname[20];
    char bdate[10];
    int day,month,year;
    printf("\n\n Enter Full Name (FirstName MiddleName LastName)  : ");
    gets(fullname); //reading fullname with spaces.
    sscanf(fullname,"%s %s %s",firstname,middlename,lastname); //reading firstname,middlename & lastname from fullname
    sprintf(shortname,"%.1s. %.1s. %s",firstname,middlename,lastname); //printing firstname and middlename initials with lastname into shortname

9. C Format Specifiers Datatype Input Function Purpose char getch()
getche()
fgetchar()
getchar()
Gets a character from keyboard as soon as it is entered, no need of ENTER key
Similar to getch(), except echoes the character on screen.
Gets the character and echoes on screen, requires ENTER key
A macro similar to fgetchar()
string
gets()
Accepts a string until enter key is pressed
Output Function
Char
putch ()
fputchar()
putchar()
Prints the character on screen
A macro works similar to putch() and fputchar()
puts()
Outputs a string to the screen

10. Disk I/O Functions There are two types of Disk I/O available
char name[5][100];
Disk I/O Functions
There are two types of Disk I/O available
Standard I/O or Stream I/O – high level
System I/O – low level
Basic difference between them is, in high level buffer management is automatically done but in other case, programmer is expected to do.
A FILE is a place on the physical disk where information is stored.
Why file is needed ?
When a program is terminated, the in-memory data is lost. Storing in a file will preserve your data even for later usage.
For a large number of data, it will take a lot of time to enter them all. However, if you have a file containing all the data, you can easily access the contents of the file using few commands in C.
Moving data from one computer to another without any changes is possible
Types of FILE 
Text File
Binary File

11. Functions for File operations
Input /
Output
Datatypes handled
Level
Usage
getc()
Input
Characters
High
putc)
fgetc()
fputc()
fscanf()
Characters, strings, numbers , records
fprintf()
fread()
fwrite()
read()
Chunk of byte data
Low
write()

12. File Opening Modes FILE *fptr; fptr = fopen(“fileopen_name”,”mode”);
For Ex:
fopen(“file_name”,”mode”);
Closing a file
fclose(fptr);
Mode
Operation
Returns
“r”/”rb”
Reading from a file
NUUL, if no file
“w”/”wb”
Writing into a file
Overwrites if file exist and new file is created otherwise
“a”/”ab”
Appending new contents at EOF
New file is created if no file exist
“r+”/”rb+”
Reading existing contents. Writing new and modifying existing ones
“w+”/”wb+”
Writing and Reading
“a+”/”ab+”
Reading existing contents. Appending new at EOF and can not modify existing ones

13. File Opening Modes with flag for low level
For Ex:
Open(“temp.dat”,OREAD|O_BINARY)
Mode
Operation
O_APPEND
Opens a file for appending
O_CREATE
Creates a file for both writing (no effect if no file is present)
O_RDONLY
Creates a file for both writing only
O_RDWR
Creates a file for both reading and writing
O_WRONLY
O_BINARY
Creates a file in binary mode
O_TEXT
Creates a file in text mode

14. Reading from a text file
/* C program to read a text file */
#include <stdio.h>
#include <stdlib.h>
int main() {
int num;
FILE *fptr;
if ((fptr = fopen("C:\\program.txt","r")) == NULL){
printf("Error! opening file");
// Program exits if the file pointer returns NULL.
exit(1); }
fscanf(fptr,"%d", &num);
printf("Value of n=%d", num);
fclose(fptr);
return 0;

15. Writing to a text file /* C program to read a text file */
#include <stdio.h>
#include <stdlib.h>
int main() {
int num;
FILE *fptr;
fptr = fopen("C:\\program.txt","w");
if(fptr == NULL)
printf("Error!");
exit(1); }
printf("Enter num: ");
scanf("%d",&num);
fprintf(fptr,"%d",num);
fclose(fptr);
return 0;

16. Reading from a bin file: fread()
for(n = 1; n < 5; ++n) {
fread(&num, sizeof(struct threeNum), 1, fptr);
printf("n1: %d\tn2: %d\tn3: %d", num.n1, num.n2, num.n3); }
fclose(fptr);
return 0;
#include <stdio.h>
#include <stdlib.h>
struct threeNum {
int n1, n2, n3; };
int main()
int n;
struct threeNum num;
FILE *fptr;
if ((fptr = fopen("C:\\program.bin","rb")) == NULL){
printf("Error! opening file");
// Program exits if the file pointer returns NULL.
exit(1); }

17. Writing to a bin file: fwrite()
for(n = 1; n < 5; ++n) {
num.n1 = n;
num.n2 = 5*n;
num.n3 = 5*n + 1;
fwrite(&num, sizeof(struct threeNum), 1, fptr); }
fclose(fptr);
return 0;
#include <stdio.h>
#include <stdlib.h>
struct threeNum {
int n1, n2, n3; };
int main()
int n;
struct threeNum num;
FILE *fptr;
if ((fptr = fopen("C:\\program.bin","wb")) == NULL){
printf("Error! opening file");
// Program exits if the file pointer returns NULL.
exit(1); }

18. File Operations – fseek()
char name[5][100];
File Operations – fseek()
Getting data using fseek()
If there are many records inside a file and need to access a record at a specific position, you need to loop through all the records before it to get the record, which will waste memory and operation time.
Syntax of fseek()
fseek(FILE * stream, long int offset, int whence)
Different Whence in fseek
Whence
Meaning
SEEK_SET
Starts the offset from the beginning of the file.
SEEK_END
Starts the offset from the end of the file.
SEEK_CUR
Starts the offset from the current location of the cursor in the file.

19. Example program: fseek()
// Moves the cursor to the end of the file
fseek(fptr, -sizeof(struct threeNum), SEEK_END);
for(n = 1; n < 5; ++n) {
fread(&num, sizeof(struct threeNum), 1, fptr);
printf("n1: %d\tn2: %d\tn3: %d\n", num.n1, num.n2, num.n3);
fseek(fptr, -2*sizeof(struct threeNum), SEEK_CUR); }
fclose(fptr);
return 0;
#include <stdio.h>
#include <stdlib.h>
struct threeNum {
int n1, n2, n3; };
int main()
int n;
struct threeNum num;
FILE *fptr;
if ((fptr = fopen("C:\\program.bin","rb")) == NULL){
printf("Error! opening file");
// Program exits if the file pointer returns NULL.
exit(1); }

20. Questions?