分类函数,所在函数库为ctype.h

int isalpha(int ch) 若ch是字母( A - Z , a - z )返回非0值,否则返回0

int isalnum(int ch) 若ch是字母( A - Z , a - z )或数字( 0 - 9 )-Classification function, where the library to ctype.h int called isalpha (int ch) if ch is a letter (' A' -'　Z ' '　a' -' z' ) returns a nonzero value, otherwise it returns 0 int isalnum (int ch ) if ch is a letter (' A' -'　Z ' ,'　a' -' z' ) or numbers (' 0 ' - ' 9' )