1isalpha() - To check Alphabets
2isnumeric() - To check Number
3isalnum() - To check both alphabates and number
1string test = "Ab4 :";
2std::isalnum(test[0]); //true
3std::isalnum(test[1]); //true
4std::isalnum(test[2]); //true
5std::isalnum(test[3]); //false
6std::isalnum(test[4]); //false