Example
/* DIFFTIME.C: This program calculates the amount of time
* needed to do a floating-point multiply 10 million times.
*/

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

void main( void )
{
time_t start, finish;
long loop;
double result, elapsed_time;

printf( "Multiplying 2 floating point numbers 10 million times...\n" );

time( &start );
for( loop = 0; loop < 10000000; loop++ )
result = 3.63 * 5.27;
time( &finish );

elapsed_time = difftime( finish, start );
printf( "\nProgram takes %6.0f seconds.\n", elapsed_time );
}

Output
Multiplying 2 floats 10 million times...

Program takes 2 seconds.

Example
/* CLOCK.C: This example prompts for how long
* the program is to run and then continuously
* displays the elapsed time for that period.
*/

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

void sleep( clock_t wait );

void main( void )
{
long i = 600000L;
clock_t start, finish;
double duration;

/* Delay for a specified time. */
printf( "Delay for three seconds\n" );
sleep( (clock_t)3 * CLOCKS_PER_SEC );
printf( "Done!\n" );

/* Measure the duration of an event. */
printf( "Time to do %ld empty loops is ", i );
start = clock();
while( i-- )
;
finish = clock();
duration = (double)(finish - start) / CLOCKS_PER_SEC;
printf( "%2.1f seconds\n", duration );
}

/* Pauses for a specified number of milliseconds. */
void sleep( clock_t wait )
{
clock_t goal;
goal = wait + clock();
while( goal > clock() )
;
}

Output
Delay for three seconds
Done!
Time to do 600000 empty loops is 0.1 seconds

Example
/* TZSET.C: This program first sets up the time zone by
* placing the variable named TZ=EST5 in the environment
* table. It then uses _tzset to set the global variables
* named _daylight, _timezone, and _tzname.
*/

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

void main( void )
{
if( _putenv( "TZ=EST5EDT" ) == -1 )
{
printf( "Unable to set TZ\n" );
exit( 1 );
}
else
{
_tzset();
printf( "_daylight = %d\n", _daylight );
printf( "_timezone = %ld\n", _timezone );
printf( "_tzname[0] = %s\n", _tzname[0] );
}
exit( 0 );
}

Output
_daylight = 1
_timezone = 18000
_tzname[0] = EST