Dividing by two integers does not return expected result

Question

I\'m currently writing a program that requires a preview of a live display, but the preview, of course, is scaled down. However, when I scale the PictureBox down, t

Answer 1

C#'s math is "correct". The understanding of what is being done is .. missing :-)

The expression 4 / 3 (of type int / int) will evaluate to the integer value 1 as it is using integer division (both operands are integers). The resulting 1 is then implicitly coerced to a double value on assignment.

On the other hand 4d / 3 will "work" (and results in a double 1.333_) because now it is double / int -> double / double (by promotion) -> double using the appropriate floating point division.

Similarly, for Height / 4 (assuming Height is an integer), these would work:

(double)Height / 4          // double / int -> double
Height / 4d                 // int / double -> double
(double)Height / (double)4  // double / double -> double

Happy coding!

Answer 2

You are doing integer division.

what you need to do is this :

private void FindOptimalRes(PictureBox picBox)
{
    double h = Height / 4D; // or Height / 4.0
    double ratio = 4D / 3D; // or 4.0 / 3.0
    picBox.Size = new Size((int)(h * ratio), (int)h); // Size is now correct [133,100]
}

when you do a mathematical operation with an integer literal (no decimal places) it is implicitly typed as an int.

Simply appending a capital D at the end of your literals (4D, 3D) will type them as doubles, and your math will be correct. Alternatively you can write 4.0, 3.0

Answer 3

You are doing integer division:

double ratio = 4 / 3; // evaluates to 1

This won't give you the value you are looking for because the decimal point is being truncated, thus evaluating to 1 instead of 1.333. At least one of the operands needs to be a double:

double ratio = 4.0 / 3.0; // evaluates to 1.333

Same goes for Height. Change the 4 to 4.0.

Answer 4

4 and 3 are both ints, so it gets turned to 1. Make them something floating-point:

double ratio = 4.0 / 3.0;

Note that you're also making the same mistake with Height (it doesn't matter right now, but it will - change it to 4.0). And if this is the actual code, why divide by four to multiply by four again?

private void FindOptimalRes(PictureBox picBox)
{
    picBox.Size = new Size(Height / 3, Height / 4);
}

Answer 5

Make sure division result is double

double ratio = (double) 4 / 3; // double division 

and no need to set your input values to double.

var num1 = // an integer number
var num2 = // an integer number

//result is integer, because of integer/integer uses 'integer division'
double result = num1 / num2; 

//result is double , because of you forced to 'double division'
double result = (double) num1 / num2;

Answer 6

Maybe you should do a decimal division and not integer division:

double h = Height / 4.0;
double ratio = 4 / 3.0;

If C# Math was off many things around the world would be off as well.