The code below actually does wait for the specified amount of time given by the variable float sec, but the terminal print behavior is incorrect. It prints: start: 0.000000 s, end: 0.000000 s, ticker: -1.#QNAN0 s ...Done waiting for: 0 s. You can test that it works against your phone's stopwatch like I have. What is wrong with my code that is making the print behavior incorrect?

Also, if there is a better implementation of what I am trying to do using standard libraries, that would be appreciated.

Thank you for your time.

/* time example */
#include <stdio.h>      /* printf */
#include <time.h>       /* time_t, struct tm, difftime, time, mktime */
#include <stdlib.h> 

void main ()
{
time_t timer;


float sec = 20;
float stopwatch;

timer = time(NULL);

do {
    time_t now;
    now = time(NULL);
    stopwatch = difftime(now,timer);
    system("clear");
    printf("start: %f s, end: %f s, ticker: %f s ...",0,sec,stopwatch);
}
while( stopwatch < sec
 );

printf("Done waiting for: %d s",stopwatch);

}