你如何一步一步地正确解释这段代码？ （编程新手）

Question

My problem is that I dont know how the compiler runs through the different if statements correctly and why he skips some in this case.

I tried checking if the conditions from start to bottom are true or false and thus find the correct output of the program. But why doesnt the program output 84 here:

if (a > c) cout << 84;
else cout << 48

Full Program:

int main()
{
  constexpr int a{8};
  constexpr int b{4};
  constexpr int c{1};

  if (a < b < c)
    if (c > b > a)
      if (a > c) cout << 84;
      else cout << 48;
    else
      if (b < c) cout << 14;
      else cout << 41;
  else
    if (b < a < c)
      if (a < c) cout << 81;
      else cout << 18;
    else
      if (b < c) cout << 17;
      else cout << 71;

  return 0;
}

The program outputs only 41. Why?

Answer 1

This statement is a nonsense:

if (a < b < c)

It will be evaluated as:

if (a < bool(b < c))

The lt/gt/eq/ne/le/ge operators are binary - ie they require two arguments. You should be doing something like:

if (a < b && b < c)

Answer 2

Firstly if you are a newbie. Don't skip braces. Now Let's go through it step by step In your first if-else. Here your a=8, b= 4, c=1. This is how your code is proceeding

if (a < b< c)  // equivalent to if(0<c) due to left associativity// firstly a<b will be evaluated which 0 and hence statement  is true as c is 1.
{
if (c > b > a) // equiavelnt to if(bool(c>b)>a) which is false as c>b is 0 hence it will reduce to if(0>c) .execution goes to else block.
{

    if (a > c)
    {
       cout << 84;
    }
    else
    {
       cout << 48;
    }
}
else
{
    if (b < c) // it is false. execution goes to else 
    {
        cout << 14;
    }
    else
    {
        cout << 41; // it is printed.
    }
}

}