how to make 69.99*100 print 6999 instead of 6998?

Question

I want to have the right 6999 but the code prints 6998, is there any way to implement it in C/C++?

#include <iostream>
using namespace std;

int main() {
 double x = 69.99;
 int xi = x*100;
 cout << xi << endl;
 return 0;
}

Answer 1

Your compiler is probably using the IEEE 754 double precision floating point format for representing the C++ data type double. This format cannot represent the number 69.99 exactly. It is stored as 69.989999999999994884. When you multiply this value with 100, the result is slightly smaller than 6999.

When implicitly converting floating-point numbers to integers, the number is always rounded towards zero (positive numbers get rounded down, negative ones get rounded up).

If you don't want to always round the result towards zero, you can change the line

int xi = x*100;

to

long xi = lround( x*100 );

which will not always round the number towards zero, but will instead always round it to the nearest integer.

Note that you must #include <cmath> to be able to use std::lround.