To get the correct results, don’t set precision greater than available for this numeric type:
#include <iostream>
#include <limits>
int main()
{
double a = 0.3;
std::cout.precision(std::numeric_limits<double>::digits10);
std::cout << a << std::endl;
double b = 0;
for (char i = 1; i <= 50; i++) {
b = b + a;
};
std::cout.precision(std::numeric_limits<double>::digits10);
std::cout << b << std::endl;
}
Although if that loop runs for 5000 iterations instead of 50, the accumulated error will show up even with this approach — it’s just how floating-point numbers work.