UVA 458 C++

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=399

#include<iostream>
#include<string>
using namespace std;
int main()
{
string input = "";
string output="";
char change;
int count = 0;
while (getline(cin, input))
{
output = "";
for (int i = 0; i <= input.length() - 1; i++)
{
change = input[i];
change = change - 7;
output = output + change;
}
cout << output << endl;
}
return 0;
}