find an error:

Question

this code swaps last and first letter of a word and adds "ay" at the end

#include <iostream>
#include <string>

int main()
{
std::string input = "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy";
int last = 0, first = 0; //input to declare enough space
char r;
std::getline(std::cin, input);

for (int i = 0; i <= input.length(); i++)
{
if (input[i] == '\0')
{
last = i - 1;
break;
}
}
r = input[last];
input[first] = input[last]; //swaps first and last letter
input[last] = r;

input[last + 1] = 'a';
input[last + 2] = 'y'; //adds an ay at the end
std::cout << input;
}

Answer 1

Instead loop, you can simply write like this

last = input.length()-1;

And
r = input[last]; //last storing
input[first] = input[last]; //again last storing in first, now last the first value..
input[last] = r; //last = last.

Instead you need

r = input[last];
input[last] = input[first];
input[first] = r;

Answer 2

thank you, now the code swaps last and first char, but adding "ay" still doesnt work

nevermind, figured it out, changed it to input = input + "ay";

Answer 3

Yes. Simply it works..
input+="ay";
Adding at index positions will not increasing string length..

Or
You can do like this

input += (input[last + 1] = 'a');
input += (input[last + 2] = 'y');