This is very simple. First, the last one. You are involved in the calculation of decimals, which is floating-point numbers. In all single-chip computers, some have floating-point numbers, such as advanced ARM, and some don't. Anything without a floating-point hardware computing module must be handled through language. The calculation of floating-point numbers is very complicated, so the last code is the largest and of course the result is the most accurate.

Let's talk about the first one first, why is it the smallest, because the single chip microcomputer will calculate 625/ 10000 first. What do you think is the result? 0.0625?

Wrong, if your res is floating-point, then the calculation result may be 0.0625, if your res is plastic, then the calculation result is 0, and here, I am sure that your res is plastic, which is equivalent to calculating tem = res*0 again, and the result is 0, that is to say, your first one is wrong and the result is constant 0.

In the second sentence, res*625 is calculated first, and then division is calculated, so there will be no constant result, so it takes more time than the first sentence.

If your result is more accurate, I suggest you use the third sentence, although it will take time.

In addition, it can be done by look-up table method, and it is not necessary to use floating-point number calculation. After all, the ability of 5 1 single chip microcomputer is relatively poor.