Objective-C: floorf( ) returns wrong value

Question

Here is the code:

    float passedPrice = 2.953;
    float placed = 1000.0; //3 decimals
    NSLog("%f", placed); // Gives 2953;
    float withNoFractions = floorf(passedPrice * placed);

The value stored in withNoFractions is 2952! It shall be 2953. What is really strange is that it works some time.

Answer 1

Many decimal floating point fractions cannot be represented as exact fractions in binary, so they have to be approximated. 2.953 is being approximated as something like 2.95299999. When you multiply by 1000, the result is 2952.99999, and when you get the floor of this, it's 2952.

To solve this, you can either use round() instead of ffloorf(), or you can add 0.5 before calling ffloorf():

float withNoFractions = floorf(passedPrice * placed + 0.5);