Why this code doesn't solve the #The Spy Life problem, while the output is the same as expected though?

Question

#include <iostream>
using namespace std;

int main() {
string input;
getline(cin, input);
string str1="";
for (int i=0;i<=input.size();i++) {
if ((input[i] >= 65 && input[i] <= 90) || (input[i] >= 97 && input[i] <= 122) || input[i] == ' ') {
str1 += input[i];
}
}
//cout << str1; // debug
//string str2="";
for (int i=0;i<=str1.size();i++) {
cout << str1[str1.size() - i];
}
//if (str2 == "tacos") cout << "yes";
//cout << sizeof(str2)<<","<<sizeof("tacos");
//cout << "tacos";

return 0;
}

Edited minutes later:
finally found that the size() method is returning the human-spoken size of the string. The size of "aaa" is actually 3 but not 2. So in my case i should write cout << str1[str1.size() - i - 1]; instead.

Answer 1

In second loop, i should start with 1 since, you're subtracting it with final output.
int i = 1;

Answer 2

thanks guys