Write about Formatted input/output Functions in C

Reading data from input device and displaying the result on the screen are the two main tasks of any programming. In ‘C’ language the input output operations are carried out by using standard functions. The programs for these functions are kept in the file . this file  must be included in the program to use these functions using the pre processor directive as: #include The i/o functions are classified into 2 types : 1. formatted functions                                 2. Unformatted functions. Formatted functions:– The formatted I/O functions read & write all types of data values. They require conversion symbol to identify the data type. scanf(_):– This is formatted i/p function which can read data from the standard i/p device into the variable in different formats by the user. The function is used to read data more than one variable at a time. Syntax:– scanf(“control string”, &arg); Ex:–scanf(“%d”,&no); 1. it reads all types of data values. 2. It is used for run time assignment of variables. 3. It requires conversion symbol to identify the data to be read by the program during execution. 4. The ampersand(&) symbol is used to indicate the memory location of the variable. So that the value read would be placed at that location. 5. The control string may contain format code, escape sequence & width specifier. 6. The format code specifies the type of input  data. 7. For each variable there must be a format code.  Syntax:scanf(“control stirng”&arg1, &arg2, . . . ,&argn); The control string specifies the field format in which the data is to be  entered & the arg.s arg1,…. arg n specify the addition of the locations where the data is stored. Control string & arguments are separated by commas. Control string contains filed specifications, which direct the interpretation of i/p data. If may include: 1. Field (or format) specifications, consisting of the conversion character %, a data type character and an optional nunmer specifying the field width. 2. Blanks, tabs, or new lines. The data character indicates the type of data that is to be assigned to the variable associated with the corresponding argument.  The field width specifies is optional. Commonly used scanf. format codes are: Code Meaning %C Read a single character %d Read decimal integer %f Read a floating point value %e Read a floating point value %O Read a octal integer %s Read a string %u Read an unsigned decimal integer %x Read a hexadecimal integer %[“] Read a string of word(s) Inputting integer numbers:– The field specification for reading a integer is : Syntax:– %wd The % sign indicates that a conversion specification follows. W is a integer number that specifies the field width of the number to be read and d, known as data type character, indicates that the number to be read is in integer mode. Ex:– scanf(“%2d%5d”, &no1, &no2); An i/p field may be skipped by specifying in the place of field width. Ex:– scanf(“%d%*d%d”, &a, &b); Will assign the data 123 456 789 Now 123 is assigned to a 456 is skipped (because of *) 789 is to b Inputting real numbers:– The field width of real numbers is not to be specified and therefore scanf reads real numbers using the simple specification %f for both the notification. Ex:– scanf(“%f%f%f”, &x, &y, &z); With the i/p data 475.1 43.21–1 678 Will assign the values:475.1 to x                                        4.321 to y and                                        678.0 to z Inputting character strings: It is done in 2 ways, by using getchar function and by using scanf function. A scanf function can input strings containing more than one character. Syntax: %ws or %wc The corresponding argument should be a pointer to a character array. %c is used to read a single character. %s is used to read words or paragraphs. Reading mixed data types:– It is possible to use one scanf statement to input a data line containing mixed mode data. in such cases, care should be exercised to ensure that the i/p data  items match the control specifications in order and type. Ex:– scanf(“%d%c%f%s”, &no, &code, & ration, name); Detection of errors in input: Only one error is encountered while reading i/p i.,e mismatch of format specifier & arguments. Rules while using scanf:– 1.Every variable to be read  must have field specification. 2. For each field specification there must be variable address Of proper  type. 3. Never end the format string with white space. It is a fatel error. 4. Scanf read until. ·         A white space character is formed. ·         The maximum no of characters have been read. ·         An error is detected. ·         The end of file is reached Formatted out put: Printf():– Pritnf function is used to print the data (or) more than one data item in different formats on the standard o/p device. Syntax:–printf(“control string”, arg1, arg2,….,argn); Control string consists of 3 types of items: 1. Characters that will be printed on the screen as they appear . 2. Format specifications that define the o/p format for display of each item. 3. Escape sequence characters such as \n, \t & \b. The control string indicates how many arguments follow & printed according to the specifications of the control string. The arguments should match in number, order and type with format specifications. Output of integer numbers: The format specification for printif on integer number is: %wd Where w specifies the minimum field width for the o/p d specifies that the value to be printed is an integer. The number is written right–justified in the given field with:
Ex:– printf(“%6d”,9876);		9 8 7 6
it is possible to force the printing to be left–justified by placing a minus sign directly after the %character.
Ex:– printf(“%–6d”,9876);		9 8 7 6
it is also possible to pad with zero’s the leading blanks by placing a 0 before the field width specifier.
Ex:– printf(“%06d”,9876);		0 0 9 8 7 6
The minus (–) & zero are known as flags.
Ex:– printf(“%d”,9876);		9 8 7 6
Out put of real numbers:– The output of a real no may be displayed in decimal notation using the following format specification %w.pf The integer w indication the minimum number of positions that are to be used for the display of the value and the integer p indicates the number of digits to be displayed after the decimal point (precision) f format specifies. We can also display a real no in exponential notation by using the specification. %w.pe
Ex:– y=98.76546 printf(“%7.4f”, y);		9 8 . 7 6 5 4
printf(“%7.2f”,y);		9 8 . 7 7
printf(“%-7.2f”, y);		9 8 . 7 7
Printing of a single character: A single character can be displayed in a desired position using the format: %wc The character will be displayed right justified in the field of w columns. We can make the display left–justified by placing a minus sign before the integer w the minus sign before the integer w. The defaults value for w  is 1.
Printing of strings: The format specification for out puting strings is similar to real numbers %w.ps Where w specifies the field width for display and p instructs that only the first P characters of the string are to be displayed. The display is right–justified. Ex:
%20s	N E W D E L H I 1 1 0 0
%20.10s	N E W D E L H I
Mixed data o/p:– Printf uses its control string to decide how many variables to be printed and what their types are. Therefore, the format specifications should match the variables in number, order and type. If there are not enough variables or if they are of the wrong type, the o/p results will be incorrect. Ex:– printf(“%d%f%s%c”,a, b, c, d);