C++，与 g++ 相等

Question

Why this condition is never true ? Both parts of the equation are integers, so there must be equality for index = 0, 10, 20, 30, 40. I am compiling this code using g++.

for(int index = 0; index < 50; index++){

        if ( (int) (10 * (  0.1 * index)  ==  (int)(10 * ( int ) ( 0.1 * index ) ) ) )
        {
                 std::cout << "equal";
        }
}

使用 MSVS 2010 编译器不会出现这些问题...

  0  0
  1  0
  2  0
  3  0
  4  0
  5  0
  6  0
  7  0
  8  0
  9  0
  10  10
  11  10
  12  10
  13  10
  14  10
  15  10
  16  10
  17  10
  18  10
  19  10
  20  20
  21  20
  22  20
  23  20
  24  20
  25  20
  26  20
  27  20
  28  20
  29  20
  30  30
  31  30
  32  30
  33  30
  34  30
  35  30
  36  30
  37  30
  38  30
  39  30
  40  40
  41  40
  42  40
  40  40
  44  40
  45  40
  46  40
  47  40
  48  40
  49  40

Answer 1

你的括号是错误的:

if ( (int) (10 * (  0.1 * index)  ==  (int)(10 * ( int ) ( 0.1 * index ) ) ) )

应该是:

if ( (int) (10 * (  0.1 * index) )  ==  (int)(10 * ( int ) ( 0.1 * index ) ) )