Formatted IO

• printf() provides formatted output;
• scanf() handles formatted input of data.

printf

Formally:

int printf(char *format, ...)

...that is...

printf( format string, argument list );

Example

printf("The littlest=%d the largest=%d\n", little, large);

thus

The littlest=3 the largest=10

printf Conversions

	argument type; printed as
%d, %i	int; decimal number
%c	int; single character
%s	char *; characters from string till \0 or number of characters given by precision
%f	double; m.dddddd where number of ds given by precision (not float)
%e, %E	double; scientific notation, m.ddddddexx (ds given by precision)

• ...there are others...

Example

• %width.precision?, e.g., %8.2f real number, 8-character field, precision of 2.

scanf

1. Formally:

   int scanf(char *format, ...)

2. Informally:

   scanf( format string, argument list );

   for example

   scanf("%d%f", &first, &second);

3. The arguments to scanf must be pointers. Compare

   scanf("%d", n); /* WRONG */ scanf("%d", &n); /* right */

   Such errors are not usually detected at compile time.

Example

Suppose we want to scan dates of the form "25/09/1965" and "25 Sep 1965" then we use, respectively,

int day, month, year; scanf("%d/%d/%d", &day, &month, &year);

and

int day, year; char monthname[20]; scanf("%d %s %d", &day, monthname, &year);

N.B. no & needed for the array.

scanf Conversions

	input data; argument type
%d	decimal integer; int
%e, %f	floating point; float (not double)
%c	characters; char *
%s	character string (not quoted); char * pointing to an array of characters large enough for the string and terminating with \0

• N.B. %f is float, not double, in contrast to printf.