Floating point comparison [duplicate]

Question

int main() {     float a = 0.7;     float b = 0.5;     if (a < 0.7)     {        if (b < 0.5) printf("2 are right");        else         printf("1 is right");     }     else printf("0 are right"); } 

I would have expected the output of this code to be 0 are right. But to my dismay the output is 1 is right why?

Answer 1

int main() {     float a = 0.7, b = 0.5; // These are FLOATS     if(a < .7)              // This is a DOUBLE     {       if(b < .5)            // This is a DOUBLE         printf("2 are right");       else         printf("1 is right");     }     else       printf("0 are right"); } 

Floats get promoted to doubles during comparison, and since floats are less precise than doubles, 0.7 as float is not the same as 0.7 as double. In this case, 0.7 as float becomes inferior to 0.7 as double when it gets promoted. And as Christian said, 0.5 being a power of 2 is always represented exactly, so the test works as expected: 0.5 < 0.5 is false.

So either:

• Change float to double, or:
• Change .7 and .5 to .7f and .5f,

and you will get the expected behavior.