Rounding down to 2 decimal places in c#

The Math.Round(...) function has an Enum to tell it what rounding strategy to use. Unfortunately the two defined won't exactly fit your situation.

The two Midpoint Rounding modes are:

1. AwayFromZero - When a number is halfway between two others, it is rounded toward the nearest number that is away from zero. (Aka, round up)
2. ToEven - When a number is halfway between two others, it is rounded toward the nearest even number. (Will Favor .16 over .17, and .18 over .17)

What you want to use is Floor with some multiplication.

var output = Math.Floor((41.75 * 0.1) * 100) / 100;

The output variable should have 4.17 in it now.

In fact you can also write a function to take a variable length as well:

public decimal RoundDown(decimal i, double decimalPlaces)
{
   var power = Convert.ToDecimal(Math.Pow(10, decimalPlaces));
   return Math.Floor(i * power) / power;
}

public double RoundDown(double number, int decimalPlaces)
{
     return Math.Floor(number * Math.Pow(10, decimalPlaces)) / Math.Pow(10, decimalPlaces);
}

There is no native support for precision floor/ceillin in c#.

You can however mimic the functionality by multiplying the number, the floor, and then divide by the same multiplier.

eg,

decimal y = 4.314M;
decimal x = Math.Floor(y * 100) / 100;  // To two decimal places (use 1000 for 3 etc)
Console.WriteLine(x);  // 4.31

Not the ideal solution, but should work if the number is small.