In Chewbacca problem 1 test case is getting failed plz help anyone

#include
using namespace std;
int main() {
char a[100];
cin>>a;

for(int i=0; a[i] != '\0'; i++){
   if(a[i] == '9'){
       i++;
   }
   int digit = a[i]-'0';  //to convert char to int digit, will give difference between ASCII values.
   if(digit>=5){
       digit=9-digit;
       a[i]=digit+'0';
   }
}
cout<<a<<endl;

return 0;

}