Why '+=' operator in double gives some random numbers?

February 19, 2023

I have project that should calculate an equation and it checks every number to see if it fits the equation. every time it pluses the number by 0.00001. but sometiomes it gets random on next decimals for example 0.000019999999997.

I even tried a breakpoint at that line. When I am right on that line it is 1.00002 for example but when I go to next line it is 1.00002999999997.

I don’t why it is like that. I even tried smaller numbers like 0.001.

List<double> anwsers = new List<double>();
double i = startingPoint;
double prei = 0;

double preAbsoluteValueOfResult = 0;
while (i <= endingPoint)
{
    prei = i;
    i += 0.001;
}

>Solution :

Added a call to Math.Round to round the result to 3 decimal places before adding it to the answers list. This ensures that the values in the list will always have exactly 3 digits past the decimal point.

List<double> answers = new List<double>();
double i = startingPoint;
double prei = 0;
double preAbsoluteValueOfResult = 0;

while (i <= endingPoint)
{
    prei = i;
    i += 0.001;
    double result = Math.Round(prei, 3);
    answers.Add(result);
}