1.isalpha
the isalpha () is used to determine whether a letter character, if the character is a non-zero return, otherwise, returns zero.
cout << isalpha ( 'a') ; // returns a nonzero
cout << isalpha ( '2') ; // returns 0
2.isalnum
isalnum () is used to determine whether a character is a number or letter, that is determined a character belongs to a ~ z || a ~ Z || 0 ~ 9.
cout << isalnum ( 'a') ; // nonzero output
cout << isalnum ( '2') ; // zero
cout << isalnum ( '.') ; // zero
3.islower
islower () is used to whether a character is a lowercase letter, i.e. whether a ~ z.
cout << islower ( 'a') ; // zero
cout << islower ( '2') ; // output 0
COUT << islower ( 'A'); // output 0
4.isupper
isupper () and islower On the contrary, it used to determine whether a character is a capital letter.
cout << isupper ( 'a') ; // returns 0
COUT <
Note: The above are the macro definition, not a real function.
Original: https: //blog.csdn.net/weixin_41162823/article/details/80172379