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

Answer 1

You're comparing 2 values of different types: a is of type float, 0.8 is of type double.

before the comparison, the float value is converted to double ... but converting from double to float and back doesn't necessarily yield the same value

if (0.8 == (double)(float)0.8) /* ... */

Answer 2

floats are not always 100% accurate, they can't be because of the way that they're stored. If you say float a = 0.8, a could really be 0.800000000001 or something like that. To compensate for this, you should use some sort of threshold. try if (fabs(a-0.8) < 1.0e-5) instead