#include 
    
     #include 
     
      int main(){    //字符分类    char a = 'A';    printf("islower(%c) is %d\n", a, islower(a));    char b = 'B';    printf("isupper(%c) is %d\n", b, isupper(b));    char c = 'C';    //是不是字母    printf("isalpha(%c) is %d\n", c, isalpha(c));    //字符转换    char d = 'D';    printf("tolower(%c) is %c\n", d, tolower(d));    char e = 'e';    printf("toupper(%c) is %c\n", e, toupper(c)