C++: How to round a double to an int? [duplicate]

add 0.5 before casting (if x > 0) or subtract 0.5 (if x < 0), because the compiler will always truncate. float x = 55; // stored as 54.999999... x = x + 0.5 - (x<0); // x is now 55.499999... int y = (int)x; // truncated to 55 C++11 also introduces std::round, which likely uses a similar logic of adding 0.5 to |x| under the hood (see the link if interested) but is obviously more robust. A follow up question might be why the float isn't stored as exactly 55. For an explanation, see this stackoverflow answer. Casting is not a mathematical operation and doesn't behave as such. Try int y = (int)round(x);