cannot convert from 'float?' to 'float

Question

I have this code:

public float? InputCutOffFrequency { get; set; }//fc

public float? InputF1 { get; set; }

public float? InputF2 { get; set; }

public float InputTransitionBand { get; set; }

public float InputFS { get; set; }

public float calcFc1(float f, float fs, float transition)
{
    float _f = f + (transition / 2);
    _f /= fs;
    return _f;
}

float fc1;
fc1 = calcFc1(InputCutOffFrequency, InputFS, InputTransitionBand);

When running this code, I get this error:

cannot convert from 'float?' to 'float

How can I fix this error?

you either supply default value like `InputCutOffFrequency??0` or ignore it via `InputCutOffFrequency.Value` — Iłya Bursov, May 24 '22 at 23:39
@IłyaBursov - Value will throw if its null, it doesnt 'ignore it' — pm100, May 24 '22 at 23:40
Does this answer your question? [How to convert C# nullable int to int](https://stackoverflow.com/questions/5995317/how-to-convert-c-sharp-nullable-int-to-int) — 41686d6564 stands w. Palestine, May 24 '22 at 23:45
`public float? InputF2 { get; set; }` to `public float InputF2 { get; set; } = 0.0f;` I prefer to initialize it to avoid nullable warnings — Cyrille Con Morales, May 25 '22 at 00:07

score 6 · Accepted Answer · edited May 24 '22 at 23:50

6

It's a nullable float so you will need to specify you want the value.

fc1 = calcFc1(InputCutOffFrequency.Value, InputFS, InputTransitionBand);

Or you can default it if it's null

fc1 = calcFc1(InputCutOffFrequency.GetValueOrDefault(0), InputFS, InputTransitionBand);

edited May 24 '22 at 23:50

Woody1193

7,252
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answered May 24 '22 at 23:39

Cody

76
3

1

Good use of the `GetValueOrDefault` method. I always forget this exists – Woody1193 May 24 '22 at 23:56

Woody1193 · Answer 2 · 2022-05-24T23:55:13.267

In C#, the ?, when used after a type, indicates that the variable associated with the type can be null or a concrete value. The function you wrote, calcFcl, has a signature that takes three floats and produces a float as output. However, when you call it, you're providing it with a float? as the first argument. Since floating-point operations with null values aren't valid, the compiler doesn't know what to do when this is the case.

There are three ways you can address this issue:

Change InputCutOffFrequency so that it is of type float instead of type float?.
Change how you call calcFc1 so that you send the value of InputCutOffFrequency instead of the nullable value:


// Force a value (this will throw an InvalidOperationException if `InputCutOffFrequency is null)
fc1 = calcFc1(InputCutOffFrequency.Value, InputFS, InputTransitionBand);

// Coalesce the value (this will force a value, but you need to be sure it's the one you want)
fcl = calcFcl(InputCutOffFrequency ?? 0, InputFS, InputTransitionBand);

Change the signature of calcFcl so that it accepts, for its first argument, a value of float? and then modify the function body so that it handles the case where the first argument is null.

public float calcFc1(float? f, float fs, float transition)
{
    float _f = (f ?? 0) + (transition / 2);
    _f /= fs;
    return _f;
}

In this case, the f ?? 0 is coalescing f to a value. Essentially, if f is null, then 0 will be used. If f is not null, then the value in f will be used.

For more information on nullable types in C#, feel free to check out the documentation.

score 1 · Answer 3 · answered May 25 '22 at 00:04

1 :

fc1 = calcFc1(InputCutOffFrequency.Value, InputFS, InputTransitionBand);

or 2 :

public float calcFc1(float f?, float fs, float transition)
{
    float _f = f + (transition / 2);
    _f /= fs;
    return _f;
}

You can change signature of nullable variable as float? in your function. [2]

Another way is getting Value of nullable variable like InputCutOffFrequency.Value [1]

cannot convert from 'float?' to 'float

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