what's the mistake?????????
#include <stdio.h>
main()
 { char num[9]; 
int i,k,u; 
gets(num); 
for(i=0;num[i]=='\0';i++) i=i--;
u=i; 
if(num[i]!=5){
if(0<=num[1]<5) k=num[0]*10^u; 
if(5<=num[1]<=9) k=num[0]++*10^u;}
else if (num[i]==5)
{
for(i=u;i==0;i--)
if(num[i]==4)
k=num[0]++*10^u;
} 
printf("%d",k); }