How do i remove a character from a string by using it's position?

In my encryption algorithm it has to pad the data if it is not a factor of the 128-bit block size. I want to remove the padding in the decryption but it will not let me do this:
Code:
...
string.at(i) = "";
...
I know there's an .erase() function but i dont know if that's the way to do it.


Thanks for the help!