2.7 INPUT / OUTPUT FUNCTIONS

There are a number of I/O functions in C, based on the data type. These functions are classified in two types:

a)      Formatted functions

                                i.            The formatted input/output functions read and write, respectively, all types of data.

                              ii.            They require format string to produce formatted results.

b)     Unformatted functions

                                i.            The unformatted input/output functions work only with character data type.

                              ii.            They do not require format conversion symbol for formatting of data types because they work only with character data type.

 

                                                                 Fig 05: I/O Functions

Formatted Functions

1)      printf( ) statement

§  The formatted output as per the programmers requirement is displayed on the screen with printf ( ).

§  The list of variables can be indicated in the printf ( ). The values of variables are printed according to the sequence mentioned in the printf ( ).

§  Syntax:

printf (“Control String”, v1, v2, …., vn);

The control string specifies the field format such as %d, %s, %f, %s, and variables as taken by the programmer. It also tells how the user wants the output to be printed. The control string is also called format string.
 

Sample Code

void main ( )

{

                                    int x = 2;

                                    float y = 5.2;

                                    char z = ‘A’;

                                    printf (“%d  %f  %c”, x, y, z);

}

OUTPUT

2  5.200000  A

§  Width and precision specifier

o   Width specifier

It sets the minimum field width for an output value. It is used along with integer and character (string) data values.

void main ( )

{

                                    int x = 55, y = 33;

                                    printf (“\n%3d”, x-y);

                                    printf (“\n%6d”, x-y);

}

OUTPUT

2

2

2

2

 

void main ( )

{

                                    printf (“\n%10s”, “abcdef”);

                                    printf (“\n%4s”, “abcdef”);

}

OUTPUT

a

b

c

d

e

f

a

b

c

d

e

f

 

o   Precision specifier

Precision results on the screen can be obtained. The precision specifier always start with a dot (.) in order to separate it from any preceding width specifier. It is used along with floating point and character (string) data values.

void main ( )

{

                                    float a = 123.456789;

                                    printf (“\n%.1f”, a);

                                    printf (“\n%.2f”, a);

                                    printf (“\n%.3f”, a);

                                    printf (“\n%.4f”, a);

}

 

OUTPUT

1

2

3

.

5

1

2

3

.

4

6

1

2

3

.

4

5

7

1

2

3

.

4

5

6

8

void main ( )

{

                                    printf (“\n%.2s”, “abcdef”);

                                    printf (“\n%.3s”, “abcdef”);

}

OUTPUT

a

b

a

b

c

 

2)      scanf( ) statement

§  The scanf ( ) statement reads all types of data values. It is used for runtime assignment of variables.

§  The scanf ( ) statement also requires conversion symbol to identify the data to be read during the execution of the program.

§  The scanf ( ) statement stops functioning when some input entered does not match with format string.

§  Syntax:

printf (“Control String”, &v1, &v2, …., &vn);

§  The scanf ( ) statement requires ‘&’ operator called address_of operator. The address_of operator points towards the memory location of the variable.

 

UNFORMATTED FUNCTIONS

1)      Character I/O functions

a.       getchar( )

§  This function reads a character-type data from standard input.

§  It reads one character at a time till the user presses the ‘enter key’.

§  Syntax:

variable_name = getchar( );

                                    e.g.

                                                char c;

                                                c = getchar( );

                                    Sample Code

                                    void main( )

                                    {

                                                char a;

                                                clrscr( );

                                                printf(“\nEnter a character:”);

                                                a = getchar( );

                                                printf(“Entered character = %c”,a);

                                    }

                                    OUTPUT

                                    Enter a character: $

Entered character = $

b.      putchar( )

§ This function prints one character on the screen ata time, read by the standard input.

§ Syntax:

putchar(variable_name);

                                    e.g.

                                                char a = ‘*’;

                                                putchar(a);

                                    Sample Code

                                    void main( )

                                    {

                                                char a = ‘9’;

                                                clrscr( );

                                                printf(“\nEntered character:”);

                                                putchar(a);

                                    }

                                    OUTPUT

                                    Entered character:9

c.       getch( ) and getche( )

§ These functions read any alphanumeric character from the standard input device.

§ The getche( ) accepts and displays the charater whereas getch( ) accepts but does not display the character.

                           

                                    Sample Code

                                    void main( )

                                    {

                                                clrscr( );

                                                printf(“\nEnter any two characters:”);

                                                getche( );

                                                getch( );

                                    }

                                    OUTPUT

                                    Enter any two characters:$

d.      putch( )

§ This function prints any alphanumeric character taken by the standard input device.

                                    Sample Code

                                    void main( )

                                    {

                                                char ch;

                                                clrscr( );

                                                printf(“\nPress any key to continue”);

                                                ch = getch();

                                                printf(“\nYou pressed:”);

                                                putch(ch);

                                    }

                                    OUTPUT

                                    Press any key to continue

                                    You pressed:@

 

2)      String I/O functions

a.       gets( )

b.      puts( )

3)      File I/O functions

a.       putc( )

b.      getc( )