C# - Rounding Down to Nearest Integer

Question

I have a C# app that is calculating some numbers. I need to round down.

var increment = 1.25;
var result = 50.45 - 23.70;    // equals 26.75
int interval = difference / increment; // result is 21.4. However, I just want 21

I have to get the interval to an int. At the same time, I cannot just use Convert.ToInt32 because of its rounding behavior. I always want the lowest whole number. However, I'm not sure how.

Solution 1

Just try this..

 int interval = Convert.ToInt32(Math.Floor(different/increment));

Solution 2

You can also just simply cast the result to int. This will truncate the number.

int interval = (int)(difference / increment);

Solution 3

Use the static Math class:

int interval = (int)Math.Floor(difference/increment);

Math.Floor() will round down to the nearest integer.

Solution 4

The Math.Floor() function should do the trick:

int interval = (int)Math.Floor(difference / increment);

See also: https://msdn.microsoft.com/de-de/library/e0b5f0xb%28v=vs.110%29.aspx

Solution 5

Convert.ToSingle(); 

is another method

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Comments

[Rob]

It returns a double = so why is there no compiler warning?

[Alexander Derck]

@Rob Just casting it to an int should do the trick, the documentation is a bit confusing "The largest integer less than or equal to d." but it does indeed return a double

[Antonín Lejsek]

Yes, this is the fastest option.

[LinusR]

Note, this is only equivalent for positive numbers. Converting to int will bring the value towards zero. If you want -1.1 to round down to -2, you need Math.Floor().

[user2455808]

what if this is a double and you have 1e300 numbers? :)