Question

I have the following code,

float a = 0.7;
if(0.7 > a)
    printf("Hi\n");
else
    printf("Hello\n");   //Line1

and

float a = 0.98;
if(0.98 > a)
    printf("Hi\n");
else
    printf("Hello\n");   //Line2

here line1 outputs Hi but Line2 outputs Hello. I assume there would be a certain criteria about double constant and float, i.e any one of them would become larger on evaluation. But this two codes clarify me that situation can be come when double constant get larger and some other times float get larger. Is there any rounding off issue behind this? If it is, please explain me. I am badly in need of this clear..
thanks advance

Answer 1

What you have is called representation error.

To see what is going on you might find it easier to first consider the decimal representations of 1/3, 1/2 and 2/3 stored with different precision (3 decimal places or 6 decimal places):

a = 0.333
b = 0.333333
a < b

a = 0.500
b = 0.500000
a == b

a = 0.667
b = 0.666667
a > b

Increasing the precision can make the number slightly larger, slightly smaller, or have the same value.

The same logic applies to binary floating point numbers.