C Programming: Input/Output Statements

INPUT/OUTPUT STATEMENTS

 

1. INPUT OUTPUT STATEMENTS

We know that input, process, output are the three essential features of computer program. The program takes some input data, processes it and gives the output.

We have two methods for providing data to the program.

• Assigning the data to the variables in a program.

• By using the Input/Output statements.

In 'C' language, two types of Input/Output statements are available, and all input and output operations are carried out through function calls. Several functions are available for input/output operations in 'C'. These functions are collectively known as the standard I/O library.

i) Unformatted Input/Output statements

ii) Formatted Input/Output statements

 

2. UNFORMATTED INPUT/OUTPUT STATEMENTS

These statements are used to Input/Output a single or Data saved in file group of characters from/to the input/output devices. Here the user cannot specify the type of data that is going to be input/output.

1. Single Character Input‒getchar() function

A Single character can be given to the computer using 'C' input library function getchar()

Syntax: char variable=getchar();

Description:

char    datatype;

variable   Any valid 'c' variable

Example:

char x  /* declaration statement*/

x=getchar();  /* input statement */

The getchar() function is written in standard I/O library. It reads a single character from a standard input device. This function do not require any arguments, through a pair of empty parentheses, must follow the statement getchar().

Example: Testing a character type.

/* Program to testing a character type */

#include<stdio.h>

main()

{

       char ch; /* Local definition */

       /* statements */

       printf("Enter any Character/Digit........");

       ch=getchar();

       if(isalpha(ch)>0)

              printf("It is a alphabet");

       else if(isdigit(ch)>0)

              printf("It is a digit");

       else

              printf("It is alphanumeric");

} /* main */

OUTPUT

1. Enter any Character/Digit......a

It is a alphabet

2. Enter any Character/Digit.......1

It is a digit

3. Enter any Character/Digit.......#

It is alphanumeric

EXPLANATION: In the above program the variable 'ch' declared as character type. The getchar() function reads only one character through the keyboard. The entered character is evaluated whether it is alphabet or digit or alphanumeric by using the respective functions. According to the entered character the output was produced.

2. Single Character Output‒putchar() function

The putchar() function is used to display one character at a time on the standard output device. This function does the reverse operation of the single character input function as discussed above.

Syntax: putchar(character variable);

Description: Character variable is the valid 'c' variable of the type of char data type.

Example:

char x; /declaration part */

putchar(x); /* output statement */

Example : Convert a Character from Lowercase to Uppercase and viceversa.

/* Program to convert a character from Lowercase to Uppercase */

#include <stdio.h>

main()

{

       char ch; /* Local definition */

       printf("Enter any alphabet either in Lower or Uppercase......");

       ch=getchar();

       if(islower(ch))

              putchar(toupper(ch)); /* tape converts the character to upper case */

       else

              putchar(tolower(ch));  /* tolower() converts the character to lower case */

} /* main */

OUTPUT:

1. Enter any alphabet either in Lower or Uppercase........s

S

2. Enter any alphabet either in Lower or Uppercase........M

m

EXPLANATION: In this program the getchar() function reads the single character from the terminal. The program finds whether the character is lower or upper case if the character is lower case then it is converts to uppercase using toupper() function, else if the character is uppercase then it is changed to lowercase using tolower() function and produced the output.

3. The getc() function

This is used to accept a single character from the standard input to a character variable.

Syntax: character variable=getc();

Description: Variable is valid 'c' variable of char data type

Example:

char c;

c=getc();

4. The putc() function

This is used to display a single character in a character variable to standard output device.

Syntax: putc(character variable);

Description: Variable is valid 'c' variable char data type

Example:

char c;

putc(c);

NOTE: The getc() and putc() are often used in file processing

5. The gets() and puts() function

The gets() function is used to read the string (string is a group of characters) from the standard input device (keyboard).

Syntax: gets(char type of array variable);

Description: Valid 'c' variable declared as one dimension char type

Example: gets(s);

The puts() function is used to display/write the string to the standard output device(Monitor).

Syntax: puts(char type of array variable);

Description: Valid 'c' variable declared as one dimension char type

Example: puts(s);

6. The getch() and getche() Functions

The getch reads a single character directly from the keyboard, without echoing to the screen. The getche reads a single character from the keyboard and echoes it to the current text window.

Syntax:

int getch(void);

int getche(void);

Return Value: Both functions return the character read from the keyboard.

7. Character Test functions

The 'C' language provides many library functions for manipulating characters. They are divided into two major groups, classifying functions and converting functions. The prototypes of these functions are in <ctype.h> headerfile. The table below summarizes some of the 'C' character test functions.

Function: Test

isalnum(ch): Is ch an alphanumeric character?

isalpha(ch): Is ch an alphabetic character?

isdigit(ch): Is ch a digit?

islower(ch): Is ch a lowercase letter?

isupper(ch): Is ch a uppercase letter?

isspace(ch): Is ch a blank space character?

tolower(ch): Convert ch to lowercase.

toupper(ch): Convert ch to uppercase.

iscntrl (ch): Is ch is ASCII control character?

isprint(ch): Is ch is printable?

isgraph(ch): Is ch is a graphic character?

ispunct(ch): Is ch is punctuation character?

isxdigit(ch): Is ch is hexadecimal digit?

 

3. Formatted Input/Output Statements

Formatted Input/Output refers to input and output, that has been arranged in a particular format. The input and output functions in C are built around the concept of a set of standard data streams being connected from each executing program to the basic input/output devices.

Example: MSSM 9293

This line contains two parts of data, that is arranged in a format, such data can be read to the format of its appearance, as the first data should be read into a variable char, the second into int. Such operation can be made possible in 'C' language by using the formatted Input/Output statements.

The following are the formatted Input/Output statements.

1. The scanf() Function

Input data can be entered into the computer using the standard input 'C' library function called scanf(). This function is used to enter any combination of input. The scanf() function is used to read information from the standard input device (keyboard), scanf() function starts with a string argument and may contain additional arguments. Any additional arguments must be pointers.

Syntax: scanf("control string", &var1, &var2,…..&varn);

Description: The Control String consists of character groups.

Example:

int n;

scanf("%d", &n);

Control string: It is the type of data that the user going to accept via the input statements, this can be formatted and always preceded with a "%' sign. The table below illustrates code formats (control strings) in Input/Output statements.

Format code

%C: Single character

%d: Decimal integer up to ‒32,768 to +32,767

%S: Strings

%f: Float values

%ld: Long integer up to ‒65,536 to + 65,535

%u: Unsigned decimal

%O: Octal number

%x: Hexadecimal number

%e: Floating point value

%h: Short integer

Each variable name (argument) must be preceded by an ampersand (&). The ('&') symbol gives the meaning "address of" the variable.

The scanf control string or placeholder consists of % at the beginning and type indicator at the end. Apart from that it can have * width indicator and a type indicator modified.

Example:

%10.2f

%10d

If input consists of 6 values and we want to ignore the middle 3 values, we can write.

The * is used to suppress input.

scanf("%d%d%*d%*d%*d%d",&i,&j,&k);

Example:

%*d

So, if our input is 10 20 30 40 50 60. It will get values 10 to i, 20 to j and 30 to k.

2. Rules for writing scanf() function

a) The control string must be preceded with (%) sign and must be within quotations. i.e., the address of variable should be passed.

b) If there is a number of input data items, items must be separated by commas and must be preceded with (&) sign except for string input.

c) The control string and the variables going to input should match with each other.

d) It must have termination with semicolon.

e) The scanf() reads the data values until the blank space in numeric input or maximum number of character have been read, or an error is detected.

Example: Program to count the number of input values using scanf() function.

/* Program to demonstrate scanf() function */

#include<stdio.h>

#include <conio.h>

void main()

{

        int i=0, j=10, k; /* Local definitions */

        /* Statements */

        printf("Enter the three values: ");

        i=scanf("%d %d %d", &j, &k, &i); scanf() reads the values*/

        printf("total values inputted %d\n", i);

        printf("The input values %d %d\n",j,k);

} /* main */

OUTPUT:

Enter the three values : 56 32 10

Total values inputted 3

The input values 56 32

EXPLANATION: This program displays the number of values inputted to the specified variables using scanf() statement.

3. The printf() function

Output data or result of an operation can be displayed from the computer to a standard output device using the library function printf(). This function used to output any combination of data. It is similar to the input function scanf(), except that it displays data rather than input.

Syntax: printf("control string", varl, var2,....... varn);

Description:

Control string is any of the following.

a) Format code character.

b) Execution character set or Escape sequences.

c) Characters/String that will be displayed

varl, var2, varn are the arguments or variables from which the data is going to output.

Example:

printf("Result is....%d", n);

printf("%f",f);

printf("%s",s);

Field width plays an important role in printf statements while producing reports in a formatted manner. Field width indicates the least number of columns that will be located to the output.

Example: i=29, its field width is %4d.

So, the four columns are allocated for i and 2 blanks are added on left side of value of i.

The output look like

If the value is more than specified column, field width is ignored and the number of column used is equal to the number of column required by the arguments.

Example: i=12345, 5 columns are required and used even if 4d specified.

If we specify * instead of field width then we have to specify additional arguments.

Example:

printf("%d\n",5,29);

printf("%d\n",10,5);

The first statement 5 is substituted for *, and it means putting the value of 29 in 5 column.

In second statement 10 is substituted for *, and it means putting value of 5 in 10 columns.

4. Rules for writing printf() function

a) Place appropriate headings in the output.

b) The variable must be separated by commas, and need not be preceded with '&' sign.

c) The control string and the variables must match in their order.

d) The control string must be in quotations and there we can also use any other text to print with data.

e) Provide blank space in between the numbers for better readability.

f) Print special messages wherever required in output.

Example 1: Program to print the number of given character using printf function.

/* Program to print the number of given character */

#include <stdio.h>

#include <conio.h>

void main()

{

        int i = 0; /* Local definitions */

        i=printf("abcde\n");

        printf("Total Number characters printed : %d\n", i);

} /* main */

OUTPUT:

abcde

Total Number characters printed: 6

EXPLANATION: This program prints the number of characters printed on the screen, the printf() statement is assigned to variable, which holds the number of characters printed on screen.

Example 2: Reading and printing data via terminals using scanf() and printf() statements.

/*Program using scanf() and printf() statements */

#include<stdio.h>

main()

{

/* Local definition */

int sno, m1,m2,m3;

char name[20]

float total, avg;

printf("Enter sno, sname, 3 sub marks");

/* Read sno, name and marks */

scanf("%d %s %d %d %d", &sno,name, &m1, &m2, &m3);

total=m1+m2+m3;

avg=total/3;

printf("Sno.....%d", sno);

printf("Name.....%s", name);

printf("Marks..... %d\t%d\t%d\t", ml,m2, m3);

printf("Total.....%f", total);

printf("Average.....%f", avg);

} /* main */

OUTPUT

Enter sno, sname, 3 sub marks

1 Mahi 90 95 98

Sno.....1

Name.....Mahi

Marks.....90 95 98

Total.....284.000000

Average.....94.333336

 

 

CASE STUDIES

(Simple Computational Problems)

 

1. Program to read two integers 'a' and 'b' and print quotient and remainder when 'a' is divided by 'b' without using the "%' operator or 'mod' function.

Suppose a=39, b=7, if 'a' is divided by 'b' quotient is '5' and remainder is 4;

Consider q=a/b, so 'q' is the quotient.

a=39, b=7, the statement q=a/b evaluates q=5

remainder = a‒q*b = 39‒5*7=  39‒35 = 4

so r=a‒q*b will calculate the remainder.

/* Program to print quotient and remainder without "%' and 'mod' function */

#include <stdio.h>

main()

{

        /* Local definition */

        int a,b,q,r;

        /*statements */

        printf("Enter a,b values.....");

        scanf("%d %d", &a,&b);

        q=a/b;

        r=a‒q*b;

        printf("Quotient is.....%d", q);

        printf("Remainder is.....%d", r);

} /* main */

OUTPUT

Enter a, b values.....39  7

Quotient is.....5

Remainder is.....4

EXPLANATION: In the above program the variables a,b,q,r are declared as integer type. The scanf() function reads values of the two variables ‘a' and 'b'. 'q' is a variable holds the result of a/b and variable 'r' holds the result of (a‒q*b). After computing quotient 'q' and remainder 'r' are printed. Note that in this program the remainder is calculated without modular division.

 

2. Write a 'C' program to calculate slope and midpoint of a line.

Let x1, y1 and x2, y2 are the coordinates of the extremities of the line.

The slope of this line is

Slope = [y2‒yl] / [x2‒x1]

For mid point of the line is

x co‒ordinate is x = [x1+x2] / 2

y co‒ordinate is y = [y2+yl] / 2

for this problem x1,y1, x2,y2 are the inputs, slope is output.

/* Program to calculates slope and midpoint of a line */

#include<stdio.h>

main()

{

      /* Local definition */

      float x,y,x1,x2, yl, y2, slope;

      *Statements */

      printf("Enter the First Point xl,yl...");

      scanf("%f%f", &x1, &yl);

      printf("Enter the Second Point x2,y2..........");

      scanf("%f%f", &x2, &y2);

      slope = (y2‒y1)/(x2‒x1); /* calculates the slope value */

      x=(x1+x2)/2.0; /* calculates x value */

      y=(y1+y2)/2.0;  /* calculates y value */

      printf("Slope is.....%f\n", slope);

      printf("Mid Point is.....%f, %f", x,y);

} /* main */

OUTPUT

Enter the First Point x1,y1... 10 20

Enter the Second Point x2,y2... 30 40

Slope is.....1.000000

Mid Point is.....20.000000, 30.000000

EXPLANATION: In the program the variables x1, y1 and x2, y2 are read through the keyboard. The variable slope holds the result of (y2‒y1)/(x2‒x1) then x is calculated by (x1+x2)/2.0 and y value is calculated by (y1+y2)/2.0. Finally the slope value is printed and midpoint is printed from the variables x and y.