一组字节，a 和 b 的值是多少

Question

program Project1;
var 
  a,b:set of byte;
  c:set of byte;
  i:integer;

begin
  a:=[3]; 
  b:=[2]; 
  c:=(a+b)*(a-b);
  FOR i:= 0 TO 5 DO
    IF i IN c THEN write(i:2);
  readln;
end.

谁能给我解释一下这段代码是怎么回事。我知道 c=3 但不明白 a 和 b 的值是多少？试过 writeln(a,b); 但给我一个错误 ...

Answer 1

好的，我将解释您可能通过调试或阅读 Pascal 教科书可能发现的内容：

行：

c := (a+b)*(a-b);

执行以下操作：

a + b is the union of the two sets, i.e. all elements that are 
      in a or in b or in both, so here, that is [2, 3];
a - b is the difference of the two sets, i.e. it is a minus the
      elements of a that happen to be in b too. In this case, no 
      common elements to be removed, so the result is the same as a, 
      i.e. [3]
x * y is the intersection of the two sets, i.e. elements that are in 
      x as well as in y (i.e. a set with the elements both have in common).

说，x := a + b; y := a - b;，那么可以分解为：

x := a + b; // [3] + [2] --> [2, 3]
y := a - b; // [3] - [2] --> [3]
c := x * y; // [2, 3] * [3] --> [3]

一组字节，a 和 b 的值是多少

Set of bytes, what are the values of a and b

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