#include  using namespace std; int main() {    int max = -1;    int number;    for(;;) {        cin >> number;        if(number == 1000) break;        if(number%10 == 0 && number > max) max = number;    }    cout << max << endl;}

#include
using namespace std;

int main() {
int a;
int max = -1000; 
cout <> a;
while (a != 1000) {
   if (a%10 == 0 && a>max) max = a;
   cout <> a;
   }
cout << "max = " << max << endl;
}

Пример:
a = 138
a = 450
a = 981
a = 190
a = 409
a = 1000
max = 450