digital_clock_v1.c

/*

    digital_clock_v1.c


    https://www.quora.com/How-do-I-print-a-digital-clock-in-C

    https://stackoverflow.com/questions/9253250/need-help-understanding-how-n-b-and-r-will-render-printf-output

    https://www.tutorialspoint.com/c-program-to-print-digital-clock-with-current-time


size_t strftime(char *str, size_t maxsize, const char *format, const struct tm *timeptr)
Formats the time represented in the structure timeptr
according to the formatting rules defined in format and stored into str.
https://www.tutorialspoint.com/c_standard_library/c_function_strftime.htm

struct tm *localtime(const time_t *timer)
Uses the time pointed by timer to fill a tm structure
with the values that represent the corresponding local time.
The value of timer is broken up into the structure tm
and expressed in the local time zone.
https://www.tutorialspoint.com/c_standard_library/c_function_localtime.htm



    You can find all my C programs at Dragan Milicev's pastebin:

    https://pastebin.com/u/dmilicev

*/

#include <stdio.h>
#include <time.h>
#include <unistd.h>

#define LEN 100
#define ESC  27


// wait (do nothing) for time in milliseconds
void wait( int milliseconds )
{
    clock_t start_time = clock();       // get start time

    // looping (do nothing) till required time is not acheived
    while ( clock() < start_time + milliseconds )
        ;                               // do nothing
}


int main (void)
{
    int ch;                             // for pressed key
    char buf[LEN];                      // string buffer
    time_t curtime;                     // current local time from system
    struct tm *loc_time;                // tm structure for local time

    printf("\n");                       // new line

    while(1)                // an infinite loop that exits with choice Ecsape, ESC (27)
    {
        while( !_kbhit() )  // rotates in that loop until some key is pressed
        {
            curtime = time (NULL);              // reset
            loc_time = localtime (&curtime);    // get current local time from system

            // fill buf with local date and time              %I hour in 12h format (01-12)
            //strftime( buf, LEN, "\r Date is %d.%m.%Y. Time is %I:%M:%S %p", loc_time );

            // or

            // fill buf with local date and time              %H hour in 24h format (00-23)
            strftime( buf, LEN, "\r Date is %d.%m.%Y. Time is %H:%M:%S ", loc_time );

            fputs (buf, stdout);        // print string buf without '\n'

            wait(1000);                 // wait 1 second = 1000 ms

            // rewrites the same line from the beginning, \r Carriage Return
            printf("\r                                        ");

        } // while( !_kbhit() )

        ch = _getch();                  // now key is pressed, read the keyboard

        if( ch == 0 || ch == 224 )      // if is pressed function key with leading 0 or 224
            ch = _getch();              // let's empty that 0 or 224

        if( ch == ESC )                 // if is pressed ESC
            return(0);                  // end of work, have to return something

    } // while(1)

   //return 0;                  // this line is never executed and is therefore commented
}