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the isalpha () is used to determine whether a character is a letter, 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 to say whether a character belongs to A ~ Z || A || the Z 0 ~ ~. 9 .
cout << isalnum ( 'a') ; // nonzero output
cout << isalnum ( '2') ; // nonzero
cout << isalnum('.');//零
3.islower
islower () is used to determine whether a lowercase character, i.e. whether A ~ Z .
cout << islower ( 'a') ; // nonzero
cout << islower ( '2') ; // Output 0
cout << islower ( 'A') ; // Output 0
4.isupper
isupper () and islower contrast, for whether a character is a capital letter.
cout << isupper ( 'a') ; // returns 0
cout << isupper ( '2') ; // returns 0
cout << isupper ( 'A') ; // returns a nonzero
Note: The above are the macro definition, not a real function.
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