Help with running a function every second.

**calCOOLus** · 11-17-2012

Hello Everyone,
This is my first post so sorry if it's bad.

Here is my code:

Code:

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




int main()
{
   int age;
   printf( "How old are you?" );
   scanf( "%d", &age );
   if ( age < 80 ) {
        printf( "Many years of learning ahead\n\n");
        }
    else {
        printf( "May the force be with you\n\n");
        }


system("PAUSE\n\n");
printf("Lets play a game.\n\n");
printf("You have %d seconds to cancel your computer from being shutdown.\n", age);
printf("Good luck.\n\n");
do
{
    printf("%d\n",age);
    sleep(1);
    age-=1;
} while(age>=0);
system("pause");
return 0;
}

Obviously the computer isn't going to be shutdown(it's to scare my brother) but every time I try to compile it, it says undefined reference to 'sleep'.
So what I want to happen is that it countsdown every second from their age.
Any help is appreciated. Thank you.

**grumpy** · 11-17-2012

Lemme guess. You are compiling under windows.

Replace the "#include <unistd.h>" line with

Code:

#ifdef __unix__
# include <unistd.h>
#elif defined _WIN32
# include <windows.h>
#define sleep(x) Sleep(1000 * x)
#endif

If this doesn't do it, you need to read the documentation with your compiler and development environment.

Bear in mind that both sleep() and Sleep() are not standard C functions.

It would also be a good idea to replace the system() calls with something else.

As to the games to scare your brother ..... I suggest you find something more worthwhile to do.

**cfanatic** · 11-17-2012

If your compiler doesn't have the sleep function, you can just make a for() loop that does nothing for 450000000 iterations, and then do a count down from age to zero by enclosing the for() loop in a do...while() loop.

If your computer is super quick, then you might need number larger than 450000000(or smaller number if your computer is slow) - play around with the number so that it coresponds to one second.

Code:

 
#include <stdio.h>

int main(void)
{
    int age = 13;
    int age_ctr;
    int ctr;

    do
    {
        for(ctr = 0; ctr < 450000000; ctr++)
        {
            ;
        }
        printf("%d\n", age);
        age--;
    } while(age > 0);
    return 0;
}

**grumpy** · 11-18-2012

Originally Posted by cfanatic

Code:

 
        for(ctr = 0; ctr < 450000000; ctr++)
        {
            ;
        }
}

There are two problems with this. Firstly, you are hardcoding an assumed processor speed.

Second, plenty of real-world compilers are smart enough to simply optimise that loop away (i.e. eliminate it completely from the executable), since it has not effect on program output. I know of at least one compiler that WOULD eliminate that loop even with all optimisation settings disabled.

**calCOOLus** · 11-18-2012

Sorry for a late reply but thank you all for your responses.
To grumpy- Thank you for your response for it worked for me.

**cfanatic** · 11-18-2012

Originally Posted by grumpy

Second, plenty of real-world compilers are smart enough to simply optimise that loop away (i.e. eliminate it completely from the executable), since it has not effect on program output. I know of at least one compiler that WOULD eliminate that loop even with all optimisation settings disabled.

Just as a matter of interest, which compilers would eliminate this loop? I have compiled it in MingW(Windows port of GCC), with no optimizations, and the loop is compiled and the executable runs the loop.

Can someone with VC++ or some other compiler run this code and give us feedback? Thanks.

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