Unexpected result of product of 2 double variables

Question

double price = 4.35; 
double quantity = 100; 
double total = price * quantity;   // Should be 100 * 4.35 = 435.00 
System.out.println(total); // Prints 434.99999999999999

Why does this happen?

[What Every Computer Scientist Should Know About Floating-Point Arithmetic](http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html). — Ted Hopp, Oct 18 '13 at 05:40

score 0 · Answer 1 · answered Oct 18 '13 at 05:31

The multiplication is working fine, but 4.35 cannot be represented exactly as a double.

Check the floating point Internal Representation.

Wiki says:-

The fact that floating-point numbers cannot precisely represent all real numbers, and that floating-point operations cannot precisely represent true arithmetic operations, leads to many surprising situations. This is related to the finite precision with which computers generally represent numbers.

score 0 · Answer 2 · answered Oct 18 '13 at 05:35

Because precision for a double is like something like:

Double-precision floating-point format is a computer number format that occupies 8 bytes (64 bits) in computer memory and represents a wide dynamic range of values by using floating point. Computers with 32-bit storage locations use two memory locations to store a 64-bit double-precision number (a single storage location can hold a single-precision number). Double-precision floating-point format usually refers to binary64, as specified by the IEEE 754 standard, not to the 64-bit decimal format decimal64.

So your value 4.35 is not exactly stored as 4.35, rather it is stored with precision

Source: Wiki

Have a look here

Unexpected result of product of 2 double variables

2 Answers2