Why the control goes in “else” part? [duplicate]

Answer 1

Floating-point numbers aren't exact values. You are not supposed to compare them using == and != . Use greater than and less than operators with some reasonably small epsilon:

if ((a > 0.79) && (a < 0.81))

Answer 2

You're using a literal, 0.8, but that doesn't necessarily mean it's a float. try using:

if (a==0.8F)

instead

Also, representing fractional parts of numbers is notoriously error-prone, due to computers internally using base-2.

Answer 3

because for floating point numbers 0.8 does not really means 0.8 but it is 0.799999999 so it happens Why it is 0.79999999
This depends on the storage of a float value. The decimal values will be stored in binary form (....,2^3,2^2,2^1,2^0,.,2^-1,2^-2,2^-3,...)

So, when 0.8 is stored in multiples of 2 as .101b(which is not 0.8 but 0.799999988).Hence its value will be less than 0.8.

if (a > 0.8) 

is also False thats why.

for your result try

if (a == 0.8f) 

Answer 4

This is because floating points can't exactly represent decimals, so it isn't exactly 0.8. And you're comparing 0.8 rounded as a float to 0.8 rounded as a decimal, which aren't necessarily the same.

Answer 5

if (a==0.8f)

Try this instead. By default, the type is consider to be double which has precision error in comparison.

Answer 6

0.8 cannot be represented accurately in binary floating-point. Your code if (a == 0.8) basically compares single-precision 0.8 with double-precision 0.8, which are not equal.

To see this for yourself, try the following code:

int main()
{
    double a = 0.8f;
    double b = 0.8;

    printf("%lX\n", *(long *)&a);
    printf("%lX\n", *(long *)&b);
}

It outputs:

3FE99999A0000000
3FE999999999999A