- 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
Reading and Writing Single Char
- 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
Formatted Input
- 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
|
Points for Scanf
- 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
Formatted Output
- 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 Spec for Integers
|
Format
|
Output
|
|
printf(“%d”,9876);
|
9876
|
|
printf(“%6d”,9876);
|
_ _9876
|
|
printf(“%2d”,9876);
|
9876
|
|
printf(“%-6d”,9876);
|
9876_ _
|
|
printf(“%06d”,9876);
|
009876
|
Real Number Output
- %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
|
Printing Characters
- %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
Printing of Chars and Strings
|
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
|
Output Format Flags
|
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
|