Unit 3. Input and Output

Input and Output Operations
Unit 3

Data Input and Output
• A program without any input or output has no
meaning.
• Input  process  Output
• Ex. marks sheet of students
• Reading the data from input devices and
displaying the result are the two main tasks of
any program.
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• Input/output functions are the links between
the user and the terminal.
• Input functions are used to read data from
keyboard are called standard input functions.
– scanf(), getchar(),getche(),getch() etc.
• Output functions are used to display the result
on the screen are called standard output
functions.
– printf(), putchar(), putch(), puts() etc.
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• In C, the standard library stdio.h provides
functions for input and output.
• The instruction #include<stdio.h> tells the
compiler to search for a file named stdio.h
and places its contents at this point in the
program.
• The contents of the header file become part
of the source code when it is compiled.
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• The input/output functions are classified into
two types –
1. Formatted functions
2. Unformatted functions
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Formatted Functions
• Formatted functions allow the input read input from
the keyboard or the output displayed on screen to be
formatted according to our requirements.
– Input function: scanf()
– Output function: printf()
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Formatted Input
• Ex: consider the following data:
– 50, 13.45, Ram
– Int, float, char variables
• This is possible using the scanf function.
• scanf stands for scan formatted.
• The built-in function scanf() can be used to enter
input data into the computer from a standard
input device.
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• The general form of scanf is,
scanf(“control string” , arg1, arg1,….. argn);
– Control string format in which data is to be
entered.
– arg1,arg2…  location where the data is stored.
 preceded by ampersand (&)
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• The control string consists of individual groups of
data formats, with one group for each input data
item.
• Each data format must begin with a percentage sign.
• General form of control string:
[whitespace character][ordinary character]%[field width] conversion character
– Whitespace characters [optional]
– Ordinary characters [Optional]
– Field width [Optional]
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#include<stdio.h>
#include<conio.h>
void main() // Whitespace characters example
{
int n1;
char ch;
clrscr();
printf("Enter a number: ");
scanf(“ %d",&n1);
printf("Enter a character: ");
scanf(“ %c",&ch);
printf("nNumber: %d t Character: %c",n1,ch);
getch();
}
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#include<stdio.h>
#include<conio.h>
Void main(){ // Ordinary characters
Int day,year,month;
clrscr();
printf(“enter day month year in DD-MM-YYY format”);
scanf(“%d-%d-%d”,&day,&month,&year);
getch();
}
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#include<stdio.h>
#include<conio.h>
void main(){ //Field width example
int d;
printf(“Enter Max 5 numbers”);
scanf(“%5d”,&d);
printf(“Entered Numbers: %d”,d);
getch();
}
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#include<stdio.h>
#include<conio.h>
void main(){ //Input String
char string[10];
printf(“Enter Your Name”);
scanf(“%s”,string);
printf(“Your Name is %s”);
getch();
}
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#include<stdio.h>
#include<conio.h>
void main(){
char string[10];
printf("Enter Your Name:");
scanf("%s",string);
printf("My Name is %s",string);
getch();
}
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• some versions of scanf() support the following
conversion specifications for strings:-
%[character]
– only characters specified within the brackets are
allowed in the input string.
%[^character]
– the character specified after the caret are not allowed
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#include<stdio.h>
#include<conio.h>
void main(){
char string[10];
printf("Enter Your Name in uppercase:");
scanf("%[A-Z]",string);
printf("Your Name is %s",string);
getch();
}
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#include<stdio.h>
#include<conio.h>
void main(){
char string[10];
printf("Enter Your Name:");
scanf("%[^n]",string);
printf("My Name is %s",string);
getch();
}
%[^n] tells the compiler to read a string until a
newline character is entered
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Reading Mixed Data Types
• printf(“enter an integer, floating number,
gender and name:”);
scanf(“%d %f %c%s”,&i,&n1,&gender,&name);
• scanf() can contain mixed mode data.
• care should be taken to ensure that the input
data items match the control specification.
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Formatted Output
• refers to the output of data that has been arranged in a
particular format.
• printf() is a built in function which is used to output data from
the computer onto a standard device i.e. screen
• General form:
printf(“control string”,arg1,arg2,.....,arg n)
• The control string consists of four types of items -
– characters that will be printed on the screen as they appear.
– format specifications that define the output format for display of each item
– escape sequence characters such as n, t etc.
– any combination of characters, format specifications and escape sequences.
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• The control string has the form:
%[flag] [field width][.precision] conversion character
• Flags [optional]
– “ – “ indicates data item to be left-justified
– “+” indicates a positive or negative sign to precede
– “0” indicates leading 0’s to appear instead of leading
blanks
• Field width[optional]
– Same as before
• Precision [optional]
– The operation of precision field depends on the type of
conversion. It must start with a period (.).
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Unformatted Functions
• Doesn’t allow user to read or display data in
desired format.
• These library functions basically deals with a
single character or a string of characters.
• The functions getchar(), putchar(),
gets(),puts(),getch(),getche(),putch() are
considered as unformatted functions.
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• getchar()
– Reads a character from a standard input device.
– It takes the form:
Character_variable= getchar();
– Character_variable is a valid C char type variable.
– When this statement is encountered, the
computer waits until a key is pressed and then
assigns this character to character_variable.
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• putchar()
– Displays a character to the standard output
device.
– Its form:
putchar(character_variable);
– Where character_variable is a char type variable
containing a character
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Void main(){
char gender;
clrscr();
printf(“Enter gender M or F”: );
gender=getchar();
printf(“Your Gender is: “);
putchar(gender);
getch();
}
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• getch() and getche()
– Reads single character the instant it is typed
without waiting for the enter key to be hit.
– getch() doesn’t print the character entered
– getche() displays the character when entered.
– General form
• character_variable=getch();
• character_variable=getche();
– In both functions, the character typed is assigned
to the char type variable character_variable.
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• putch()
– The function putch() prints a character onto the
screen
– General form
• putch(character_variable);
– Character variable is a char type.
NOTE: These three functions are defined under the
standard library functions conio.h
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void main(){
char ch1, ch2;
clrscr();
printf("Enter 1st character: ");
ch1=getch();
printf("n Enter 2nd character");
ch2=getche();
printf("n first character: ");
putch(ch1);
printf("nSecond character: ");
putch(ch2);
getch();
}
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• gets()
– Used to read string of text, containing
whitespaces, until a new line character is
encountered.
– General form
gets(string_variable);
• puts()
– Used to display the string onto the terminal
– General form:
puts(string_variable);
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void main()
{
char name[20];
clrscr();
printf("Enter your name:");
gets(name);
printf("Your Name is: ");
puts(name);
getch();
}
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Unit 3. Input and Output

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Unit 3. Input and Output