Length of a String
str.length();
Check if a character is alphanumeric
#include <ctype.h>
isalnum(c);
Convert a character to upper case
#include <ctype.h>
toupper(c);
Append a character to String
str.push_back(c);
Convert string to int
stoi(string);
Convert int to string
to_string(integer);
Append String to String
str1.append(str2);
Append anything to String
stringstream ss;
ss << integer;
ss << string;
ss << character;
ss.str();
Reverse a String
reverse(str.begin(), str.end());
Erase characters in string
str.erase(index_of_first_char_to_remove, num_chars)