there are 216 = 65,536 unicode characters.
Since this character set is very large and its structure very complex, in
this class
we will use only the subset of unicode that includes all the
ASCII (pronounced "Ask E") there are 28 = 256
ASCII characters, of which we will still use a small subset containing
alphabetic, numeric, and some special characters.
We can describe the structure of this character set quite simply in EBNF,
using only alternatives in the right hand sides.
lower-case <= a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z
upper-case <= A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z
alphabetic <= lower-case | upper-case
numeric &nbsp &nbsp <= 0|1|2|3|4|5|6|7|8|9
alphanumeric <= alphabetic | numeric
special &nbsp &nbsp &nbsp <= !|%|^|&|*|(|)|-|+|=|{|}|||~|[|]|\|;|'|:|"||?|,|.|/|#|@|`|_
graphic &nbsp &nbsp <= alphanumeric | special
In the special rule, the bracket/brace characters stand for themselves
(not EBNF options nor repetitions) and one instance of the vertical bar
stands for itself too: this is the problem one has when the character set
of the language includes special characters that also have meanings in
White space consists of spaces (from the space bar), horizontal and vertical
tabs, line terminators (newlines and formfeeds): all are non-printing
characters, so we must describe them in English.
White space and tokens are closely related: we can use white space to force
the end of one token and the start of another token (i.e., white space is
used to separate tokens).
For example XY is considered to be a single token, while X Y
is considered to be two tokens.
The "white space separates tokens" rule is inoperative inside
String/char literals, and comments (which are all discussed
Adding extra white space (e.g., blank lines, spaces in a line -often for
indenting) to a program changes its appearance but not its meaning to Java:
it still comprises exactly the same tokens in the same order.
Programmers mostly use white space for purely stylistic purposes: to
isolate/emphasize parts of programs and to make them easier to read and
understand.
Just as a good comedian know where to pause a good
programmer knows where to put white space when writing code.
Classify each of the following numeric literals as int, or double, or
illegal (neither); write the equivalent value of each double without using
E for each illegal literal, write a legal one with the "same" value.
What is the difference between 5, 5., five,
'5', and "5"?
What is the difference between true and "true"?
Write a String literal that includes the characters
I've said a million times, "Do not exaggerate!"
How does Java classify each of the following lines
&nbsp &nbsp "//To be or not to be"
&nbsp &nbsp //"To be or not to be"
Does the following line contain one comment or two?
&nbsp &nbsp//A comment //Another comment?
Explain whether X/**/Y is equivalent to XY or X &nbsp Y.
Tokenize the following Java Code (be careful): -15
Tokenize the following line of Java code: identify every Java token as either an
Identifier, Keyword, Separator, Operator, Literal (for any literal, also specify its type), or Comment.
Which (if any) identifiers are keywords?
int X = Prompt.forInt("SSN",0,);
//Filter && use
Choose an appropriate type to represent each of the following pieces of information
the number of characters in a file
a time of day (accurate to 1 second)
the middle initial in a name
whether the left mouse button is currently pushed
the position of a rotary switch (with 5 positions)
the temperature of a blast furnace
an indication of whether one quantity is less than, equal to or greater than another
the name of a company
This problem (it is tricky, so do it carefully) shows a difficulty with using
Block-Oriented comments.
Tokenize the following two lines of Java code: identify every token as either an
Identifier, Keyword, Separator, Operator, Literal, or Comment. What problem arises?
/* Initialize x and y to
their starting values */
Rewrite the code shown above with Line-Oriented comments instead, to avoid this problem.
How can our use of my Java preferences help us avoid this error?
This problem (it is tricky, so do it carefully) shows another difficulty with using
Block-Oriented comments.
Tokenize the following Java code: identify every token as either an
Identifier, Keyword, Separator, Operator, Literal, or Comment. What problem arises?
here is an outer
comment with an
/* inner comment inside */
and the finish of the outer
comment at the end
Rewrite the code shown above with Line-Oriented comments instead, to avoid this problem.
How can our use of my Java preferences help us avoid this error?
Explain why language designers are very reluctant to add new keywords
to a programming language.
Hint: what problem might this cause in already-written programs?time, _time32, _time64
time, _time32, _time64
Expand the table of content
time, _time32, _time64
Visual Studio 2015
Get the system time.
time_t time(
time_t *timer
__time32_t _time32(
__time32_t *timer
__time64_t _time64(
__time64_t *timer
timerPointer to the storage location for time.Return the time as seconds elapsed since midnight, January 1, 1970, or -1 in the case of an error.The time function returns the number of seconds elapsed since midnight (00:00:00), January 1, 1970, Coordinated Universal Time (UTC), according to the system clock. The return value is stored in the location given by timer. This parameter may be NULL, in which case the return value is not stored.time is a wrapper for _time64 and time_t is, by default, equivalent to __time64_t. If you need to force the compiler to interpret time_t as the old 32-bit time_t, you can define _USE_32BIT_TIME_T. This is not recommended because your application may fail after January 18, 2038; the use of this macro is not allowed on 64-bit platforms.RoutineRequired headertime, _time32, _time64 C: &time.h&, C++: &ctime& or &time.h&For additional compatibility information, see
in the Introduction.
// crt_times.c
// compile with: /W3
// This program demonstrates these time and date functions:
_localtime64_s
_gmtime64_s
_strtime_s
_strdate_s
// Also the global variable:
// Turn off deprecated unsafe CRT function warnings
#define _CRT_SECURE_NO_WARNINGS 1
#include &time.h&
#include &stdio.h&
#include &stdlib.h&
#include &sys/types.h&
#include &sys/timeb.h&
#include &string.h&
int main()
char tmpbuf[128], timebuf[26], ampm[] = "AM";
struct tm today, gmt, xmas = { 0, 0, 12, 25, 11, 93 };
// Set time zone from TZ environment variable. If TZ is not set,
// the operating system is queried to obtain the default value
// for the variable.
// Display operating system-style date and time.
_strtime_s( tmpbuf, 128 );
printf( "OS time:\t\t\t\t%s\n", tmpbuf );
_strdate_s( tmpbuf, 128 );
printf( "OS date:\t\t\t\t%s\n", tmpbuf );
// Get UNIX-style time and display as number and string.
time( &ltime );
printf( "Time in seconds since UTC 1/1/70:\t%lld\n", (long long)ltime );
err = ctime_s(timebuf, 26, &ltime);
printf("ctime_s failed due to an invalid argument.");
printf( "UNIX time and date:\t\t\t%s", timebuf );
// Display UTC.
err = _gmtime64_s( &gmt, &ltime );
printf("_gmtime64_s failed due to an invalid argument.");
err = asctime_s(timebuf, 26, &gmt);
printf("asctime_s failed due to an invalid argument.");
printf( "Coordinated universal time:\t\t%s", timebuf );
// Convert to time structure and adjust for PM if necessary.
err = _localtime64_s( &today, &ltime );
printf("_localtime64_s failed due to an invalid argument.");
if( today.tm_hour &= 12 )
strcpy_s( ampm, sizeof(ampm), "PM" );
today.tm_hour -= 12;
if( today.tm_hour == 0 )
// Adjust if midnight hour.
today.tm_hour = 12;
// Convert today into an ASCII string
err = asctime_s(timebuf, 26, &today);
printf("asctime_s failed due to an invalid argument.");
// Note how pointer addition is used to skip the first 11
// characters and printf is used to trim off terminating
// characters.
printf( "12-hour time:\t\t\t\t%.8s %s\n",
timebuf + 11, ampm );
// Print additional time information.
_ftime( &tstruct ); // C4996
// Note: _ consider using _ftime_s instead
printf( "Plus milliseconds:\t\t\t%u\n", tstruct.millitm );
printf( "Zone difference in hours from UTC:\t%u\n",
tstruct.timezone/60 );
printf( "Time zone name:\t\t\t\t%s\n", _tzname[0] ); //C4996
// Note: _ consider using _get_tzname
printf( "Daylight savings:\t\t\t%s\n",
tstruct.dstflag ? "YES" : "NO" );
// Make time for noon on Christmas, 1993.
if( mktime( &xmas ) != (time_t)-1 )
err = asctime_s(timebuf, 26, &xmas);
printf("asctime_s failed due to an invalid argument.");
printf( "Christmas\t\t\t\t%s\n", timebuf );
// Use time structure to build a customized time string.
err = _localtime64_s( &today, &ltime );
printf(" _localtime64_s failed due to invalid arguments.");
// Use strftime to build a customized time string.
strftime( tmpbuf, 128,
"Today is %A, day %d of %B in the year %Y.\n", &today );
printf( tmpbuf );
Not applicable. To call the standard C function, use PInvoke. For more information, see .
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