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 1 string a = "4546311.670";
 2 string b = "318241.810";
 3 WriteText("float:");
 4 WriteText(a);
 5 WriteText("+");
 6 WriteText(b);
 7 float fa = Convert.ToSingle(a);
 8 float fb = Convert.ToSingle(b);
 9 WriteText("=");
10 float fc = fa + fb;
11 WriteText(string.Format("{0:0.00}",fc));
12 decimal da = Convert.ToDecimal(a);
13 decimal db = Convert.ToDecimal(b);
14 WriteText("\n\r");
15 WriteText("decimal:");
16 WriteText(a);
17 WriteText("+");
18 WriteText(b);
19 WriteText("=");
20 WriteText((da + db).ToString());

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以上放到.ashx中，直接输出如下:
float:4546311.670+318241.810=4864554.00

decimal:4546311.670+318241.810=4864553.480
1)float真的会有误差
2)尤其奇怪的点是:单步执行中可以看到的fc=4864553.50 可是输出的时候{0:N2} {0:0.00}都无法输出4864553.50.