–  IO is not part of C syntax
–  Several functions becomes standard for IO are called Standard IO Library in C
–  The printf and scanf are library functions
–  The stdio.h file and its inclusion in the program using include directive
–  Other headers such as math.h etc

• The ch = getchar() function and problems associated with input stream
• The isalpha(), isdigit(), isalnum(), islower(), isupper(), isprint(), isspace(), ispunct(), etc. functions and ctype.h file
• The putchar(<char>) function
• putchar(‘\n’) jumps to next line

• Scanf(<control string>,arg1,arg2,agr3…)
• Control string specifies the field format in which the data is to be entered
• arg1, arg2 etc specifies the locations or addresses where the data is to be stored
• Control string contains field specifications which directs the interpretation of input
• Control String may include
  • Field or format specs consisting of conversion char (%), a data type specifier,  and optional width field
  • Blanks, tabs and newlines
• %wd for integers, %f for float, %lf for double,
• * as width for skipping a field
• %ws or %wc for char strings
• Scanf returns no of items read

Code	Meaning	Code	Meaning
%c	Single Char	%i	Decimal, hex or octal int
%d	Decimal Integer	%o	Octal integer
%e	Floating point	%s	String
%f	Floating point	%u	Unsigned int
%g	Floating point	%x	Hexadecimal int
%h	Short int	%[/^..]	String of words

• All args except CS, must be pointer to vars
• Format specs should match the args in order
• Input data items to be separated by spaces and match the variables receiving in order
• Invalid mismatch will terminate scanf
• Scanf ignores line boundaries
• Unread data items are part of next read
• W should be large enough

• printf(“control” string, arg1,arg2…)
• Control string may contain following
  • Chars to be printed on the screen as it is
  • Format specs for each item to be displayed
  • Escape sequences chars such as \n, \t etc
• The args should match the specs in number order and type
• Form of format spec is %w.p type-specs

Format	Output
printf(“%d”,9876);	9876
printf(“%6d”,9876);	_ _9876
printf(“%2d”,9876);	9876
printf(“%-6d”,9876);	9876_ _
printf(“%06d”,9876);	009876

• %w.p f  or %w.p e is the format spec
• w is minimum number of position used to display the value
• p is number of digits displayed after decimal point
• If E is used Output will contain E
• If g or G, it picks up shorter f or e(E)
• The value, when printed, is rounded to p decimal places and printed right justified in w columns
• Leading blanks and trailing zeroes will appear as necessary
• The default precision is 6 decimal places
•  w >= p +7 for e or E
• printf (“%.*f”, width, precision, number)

Format Specs for Real Numbers

Format	Output
printf(“%7.4f”,y)	98.7654
printf(“%7.2f”,y)	_ _ 98.77
printf(“%-7.2f”,y)	98.77_ _
printf(“%f”,y)	98.7654
printf(“10.2e”,y)	_ __ 9.88e+01
printf(“%11.4e”,-y)	-9.8765e+01
printf(“%-10.2e”,y)	9.88e+01_ _
printf(“%e”,y)	9.876540e+01

• %w.ps for strings where w is the field width of display and p is no of chars to be printed
• It is printed right justified !
• %wc can print right justified in width of w columns
• Default value of w is 1, if precedes with – sign, it prints the data right justified

Specification	Output
%s	New Delhi 110001
%20s	_ _ _ _ New Delhi 110001
%20.10s	_ _ _ _ _ _ _ _ _ _ _ _ New Delhi
%.5s	New D
%-20.10s	New Delhi _ _ _ _ _ _ _ _ _ _ _ _ _ _
%5s	New Delhi 110001

Flag	Meaning
–	Output left justified within the field.
+	Signed numeric item will be preceded by +/-
0	Causes leading zeros to appear
#(with o or x)	Octal and hex items to be preceded with 0 or 0x
# (with e f or g)	Causes a decimal point to be present in all floating point numbers. In g prevents truncation of trailing zeros