what's the difference between printf a floating-point variable and constant?

Question

Here's my code:

float x = 21.195;
printf("%.2f\n", x);
printf("%.2f\n", 21.195);

I would expect both print statements to have identical output, but instead, the first prints 21.19, and the second prints 21.20.

Could someone explain why the output is different?

Answer 1

The values are different. The first is a float, which is typically 4 bytes. The second is a double, which is typically 8 bytes.

The rules for rounding are based on the third digit after the decimal place. So, in one case, the value is something like 21.19499997 and the other 21.1950000000001, or something like that. (These are made up to illustrate the issue with rounding and imprecise numeric formats.)

Answer 2

By default 21.195 is a double.

If you want a float, write :

21.195F

or

(float)21.195

Regards