Streams

scanf, gets and getchar read from the standard input stream.
printf, puts and putchar write to the standard output stream.
The standard input stream normally is connected to the keyboard.
The standard output stream normally is connected to the screen.
There is a third standard stream also connected to the screen for errors, it’s called the standard error stream.
Inputs and outputs are processed with streams which are sequence of bytes.
- In input operations, the bytes flow from a device: Keyboard, Disk Drive, network connection, etc.
- In output operations, bytes flow from main memory to a device: display screen, a printer, a network connection, etc.

Printing Integers

Specifier	Description	Example Output
`%d`	Signed decimal integer	`123`
`%i`	Signed decimal integer (same as `%d`)	`123`
`%u`	Unsigned decimal integer	`123`
`%o`	Unsigned octal	`173`
`%x`	Unsigned hexadecimal (lowercase)	`7b`
`%X`	Unsigned hexadecimal (uppercase)	`7B`
`%hhd`	Signed `char`	`127`
`%hhu`	Unsigned `char`	`255`
`%hd`	Signed `short`	`32767`
`%hu`	Unsigned `short`	`65535`
`%ld`	Signed `long`	`2147483647`
`%lu`	Unsigned `long`	`4294967295`
`%lld`	Signed `long long`	`9223372036854775807`
`%llu`	Unsigned `long long`	`18446744073709551615`
`%jd`	Signed `intmax_t`	Depends on system
`%ju`	Unsigned `uintmax_t`	Depends on system
`%zd`	Signed `size_t`	Depends on system
`%zu`	Unsigned `size_t`	Depends on system
`%td`	Signed `ptrdiff_t`	Depends on system
`%tu`	Unsigned `ptrdiff_t`	Depends on system

Specifier	Description	Example Output
`%f`	Decimal notation (fixed-point)	`123.456000`
`%F`	Decimal notation (uppercase, fixed-point)	`123.456000`
`%e`	Scientific notation (lowercase 'e')	`1.234560e+02`
`%E`	Scientific notation (uppercase 'E')	`1.234560E+02`
`%g`	Shortest representation of `%f` or `%e`	`123.456` or `1.23e+02`
`%G`	Shortest representation of `%F` or `%E`	`123.456` or `1.23E+02`
`%a`	Hexadecimal floating-point (lowercase)	`0x1.edd2f2p+6`
`%A`	Hexadecimal floating-point (uppercase)	`0X1.EDD2F2P+6`
`%Lf`	`long double` in decimal notation	Depends on system
`%Le`	`long double` in scientific notation	Depends on system
`%Lg`	`long double` in shortest representation	Depends on system

Specifier	Description	Example Output
`%c`	Character	`A`
`%s`	String	`"Hello"`
`%p`	Pointer address	`0x7ffee5b7a8c0`
`%n`	Stores number of characters printed so far	(Stores value in an integer variable)
`%%`	Prints a literal `%`	`%`

Flag	Description	Example (`%8d`, `%.2f`, etc.)	Output (if `value = 42` or `value = 3.14159`)
`-`	Left-align the output within the given width	`%-8d`	`"42 "` (padded with spaces)
`+`	Always show sign (`+` or `-`) for numbers	`%+d`	`+42`
	Add a space before positive numbers	`% d`	`" 42"` (instead of just `42`)
`0`	Zero-padding instead of spaces	`%08d`	`"00000042"`
`#`	Alternate form (prefix for hex, octal, etc.)	`%#x`, `%#o`, `%#f`	`"0x2a"`, `"052"`, `"3.141590"`
`.`	Precision specifier (decimal places for floats)	`%.2f`	`"3.14"`
`*`	Width or precision from an argument	`%d` (`printf("%d", 8, 42);`)	`" 42"`

Escape Sequence	Description	Example Usage	Output
`\n`	Newline	`printf("Hello\n");`	`"Hello"` (new line after)
`\t`	Tab (horizontal)	`printf("A\tB\n");`	`"A B"`
`\r`	Carriage return	`printf("Hello\rHi");`	`"Hi"` (overwrites "Hello")
`\b`	Backspace	`printf("A\bB\n");`	`"B"` (A is erased)
`\f`	Form feed (page break)	`printf("A\fB\n");`	`"A"` `"(page break) B"`
`\v`	Vertical tab	`printf("A\vB\n");`	`"A"` (vertical spacing) `"B"`
`\\`	Backslash	`printf("\\n");`	`"\n"` (prints as text)
`\'`	Single quote	`printf("\'");`	`'`
`\"`	Double quote	`printf("\"");`	`"`
`\?`	Question mark (avoid trigraphs)	`printf("\?");`	`?`
`\0`	Null character (string terminator)	`printf("A\0B\n");`	`"A"` (stops at `\0`)
`\xhh`	Hexadecimal character	`printf("\x41");`	`"A"` (ASCII 65)
`\ooo`	Octal character	`printf("\101");`	`"A"` (ASCII 65)

Specifier	Description	Example Input	Example Code
`%d`	Reads a signed integer	`42`	`scanf("%d", &num);`
`%i`	Reads an integer (auto base detect: decimal, octal, hex)	`0x2A`	`scanf("%i", &num);`
`%u`	Reads an unsigned integer	`100`	`scanf("%u", &unum);`
`%o`	Reads an octal integer	`052`	`scanf("%o", &octal);`
`%x`	Reads a hexadecimal integer	`0x2A`	`scanf("%x", &hex);`
`%f`	Reads a floating-point number	`3.14`	`scanf("%f", &flt);`
`%lf`	Reads a `double`	`3.14159`	`scanf("%lf", &dbl);`
`%Lf`	Reads a `long double`	`3.1415926535`	`scanf("%Lf", &ldbl);`
`%c`	Reads a single character	`A`	`scanf(" %c", &ch);`
`%s`	Reads a string (until whitespace)	`Hello`	`scanf("%s", str);`
`%p`	Reads a memory address (pointer)	`0x123abc`	`scanf("%p", &ptr);`
`%n`	Stores number of characters read	(N/A)	`scanf("%d%n", &num, &count);`