关于C#：为什么四舍五入时.5变成1.0？应该不是0.5吗？

Why does .5 become 1.0 when rounding? Shouldn't it be 0.5?

我正在尝试学习C。
我正在使用Mac xCode v.4.1.1
在MacBook Pro上(13英寸，2012年中)
处理器：2.9 GHz双核Intel Core i7
内存：8GB

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while (c < .9)
{
std::cin >> c;
std::cout <<"\
c =" << c << '\
';
array.push_back(c);
c = round ((c *10)/10);
std::cout <<"After rounding, c =" << c << '\
';
}
std::cout <<"\
Size of the vector \'array\' =" << array.size() << '\
';
for (int i = 0; i < array.size(); i ++ )
{
std::cout <<"\
array[" << i <<"] =" << array[i] << std::endl;
}

我的结果：

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.1

c = 0.1
After rounding, c = 0
.2

c = 0.2
After rounding, c = 0
.3

c = 0.3
After rounding, c = 0
.4

c = 0.4
After rounding, c = 0
.5

c = 0.5
After rounding, c = 1

Size of the vector 'array' = 5

array[0] = 0.1

array[1] = 0.2

array[2] = 0.3

array[3] = 0.4

array[4] = 0.5
Program ended with exit code: 0