# include "stdio.h"
 void sub1(char a,char b)
 { char c;   c=a; a=b; b=c; }
 void sub2(char *a,char b)
{ char c;   c=*a; *a=b; b=c; }
 void sub3(char *a,char *b)
{ char c;   c=*a; *a=*b; *b=c; }
void main()
 { char a,b;   a='A'; b='B';  
 sub3(&a,&b); putchar(a); putchar(b);
  sub2(&a,b);  putchar(a); putchar(b);
  sub1(a,b);   putchar(a); putchar(b);
}  答案为什么会是BAAAAA