C# Math.Round Issue

Question

I am having trouble rounding a number in C#. Here is my code:

public static double GetHighTargetHR (string birthdate, string examDate)
{
  double HighTargetHR = 0;
  double age;
  double constant = 220;

  age = CalculateAge(birthdate, examDate);

  if (age > 0)
  {
    HighTargetHR = ((constant - age) * 0.8);
    Math.Round(HighTargetHR, 0, MidpointRounding.AwayFromZero);
  }

  return HighTargetHR;
}

This patient's age is 26. So 220-26 = 194 * 0.8 = 155.20

I want the code to return 155. No matter what I change on the Math.Round function, it returns 155.20. How can I make it return an even number?

`Math.Round()` returns the rounded value. You're ignoring the return value. — CodeCaster, Nov 27 '17 at 15:17
As Pac0 and CodeCaster mentioned, you're not returning the result of your rounding call, you're just throwing it away. — Blair Scott, Nov 27 '17 at 15:18
`Int`s are value types. They are not passed by reference (like reference types) into methods so cannot be manipulated. Hence the method returns a value. See [What is the difference between a reference type and value type in c#?](https://stackoverflow.com/questions/5057267/what-is-the-difference-between-a-reference-type-and-value-type-in-c) — Liam, Nov 27 '17 at 15:19
@Liam Reference types or value types are not passed by reference unless `ref` our `out` is specified. — Magnus, Nov 27 '17 at 15:22

score 2 · Accepted Answer · answered Nov 27 '17 at 15:17

2

You have to affect the result of Math.Round to the variable. Otherwise, it is simply discarded.

 HighTargetHR = Math.Round(HighTargetHR, ...);

answered Nov 27 '17 at 15:17

Pac0

21,465
8
65
74

score 0 · Answer 2 · answered Nov 27 '17 at 15:19

You need to assign the result of the function you are using (Math.Round):

HighTargetHR = Math.Round((constant - age) * 0.8, 0, MidpointRounding.AwayFromZero);

A function returns a value; so, when you use some function, you have to assign its returned value to a variable.

score -1 · Answer 3 · edited Nov 27 '17 at 15:20

-1

You are missing to use the return type of round function.

HighTargetHR = Math.Round(HighTargetHR, 0, MidpointRounding.AwayFromZero);

edited Nov 27 '17 at 15:20

Liam

27,717
28
128
190

answered Nov 27 '17 at 15:20

Manish Dubey

706
4
17

C# Math.Round Issue

3 Answers3