localtime question

[Mipam]

Hi,

I tried to display the time from yesterday by this little program

#include <stdio.h>
#include <sys/time.h>

time_t tval;

int main()
{
struct timeval tv;
struct timeval tv_current;
if (gettimeofday(&tv_current, NULL) == -1)
        err(1, "Could not get local time of day");
tv.tv_sec = tv_current.tv_sec-86400;
printf("%s\n", ctime(tv.tv_sec) );
}

But at compilation it complains:

tijd.c: In function `main':
tijd.c:15: warning: passing arg 1 of `ctime' makes pointer from integer 
without a cast

What am i doing wrong?
Bye,

Mipam.