Please note that the atoi function can only convert strings that represent valid integer values. If the input string does not represent a valid integer, the behavior of atoi is undefined. It is also recommended to use safer alternatives such as strtol or sscanf to parse integers from strings. Also, in this code, the input index is assumed to be within the bounds of the string. It is recommended to add checks to ensure that the index is not out of bounds, to avoid accessing memory that is outside the bounds of the string.