In printf, you only reference the variable, not the address of the variable i.e. fyear not &fyear.
#include <stdio.h>
int main(){
int calclus, fyear;
do{
printf (" enter first year\n");
scanf ("%d" , &fyear);
if (((fyear % 4 == 0) && (fyear % 100!= 0)) || (fyear%400 == 0))
printf("%d is a leap year", fyear);
else
printf( "%d is not a leap year", fyear);
}
while(fyear < 999);
return 0;
}