https://www.geeksforgeeks.org/top-50-string-coding-problems-for-interviews/

• playing with characters test logic of programmer very well
• understanding of C++ Standard Template Library(STL) also increase
• frequently asked string coding questions in every coding round

• 48 to 57 - Number
• 65 to 90 - uppercase [(s[0]>='a'&&s[0]<='z']
• 97 to 122 - lowercase [(s[0]>='A'&&s[0]<='Z']
• lowercase = lowercase + 32

• toupper:- (char)tolower(s[i]);
• tolower:- (char)toupper(s[i]);

Transform:-

• transform(s.begin(), s.end(), s.begin(), ::tolower);

• transform(s.begin(), s.end(), s.begin(), ::toupper);

• Find:- s1.find(s2[i])!=string::npos:- it means <find s2[i] in s1> is present

• token:- stringstream ex:
  string s = "geeks for geeks"; stringstream ss(s); // Used for breaking words
  string word; // to store individual words
  while (ss >> word)
  cout << word << endl;
  

• next_permutation()