Why Do Casting Floats to Ints in C# Produce Different Results Depending on the Method?

Differences in coercing floating point numbers to integers in C#: the conversion method affects the results

In C#, floating point arithmetic can have unexpected behavior when casting the result to an integer. Consider the following code snippet:

<code class="language-csharp">int speed1 = (int)(6.2f * 10);
float tmp = 6.2f * 10;
int speed2 = (int)tmp;</code>

Theoretically, speed1 and speed2 should produce the same value, but surprisingly, the results are different:

<code>speed1 = 61
speed2 = 62</code>

Why is this happening?

The crux of the problem is floating point arithmetic, which may introduce rounding errors. In (int)(6.2f 10), the value 6.2f 10 (approximately 61.999998) is truncated to an integer, resulting in 61.

In contrast, in int speed2 = (int)tmp, the value 6.2f * 10 is first rounded to the nearest floating point value, which is 62. This rounded value is then converted to an integer, resulting in 62.

To ensure predictable behavior, it is generally recommended to use Math.Round or similar functions for rounding operations, rather than relying on implicit conversions.

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