Type of Conditional Expression Cannot Be Determined Because There Is No Implicit Conversion Between 'Int' and <Null>

Type of conditional expression cannot be determined because there is no implicit conversion between 'int' and null

The spec (§7.14) says that for conditional expression b ? x : y, there are three possibilities, either x and y both have a type and certain good conditions are met, only one of x and y has a type and certain good conditions are met, or a compile-time error occurs. Here, "certain good conditions" means certain conversions are possible, which we will get into the details of below.

Now, let's turn to the germane part of the spec:

If only one of x and y has a type, and both x and y are implicitly convertible to that type, then that is the type of the conditional expression.

The issue here is that in

int? number = true ? 5 : null;

only one of the conditional results has a type. Here x is an int literal, and y is null which does not have a type and null is not implicitly convertible to an int¹. Therefore, "certain good conditions" aren't met, and a compile-time error occurs.

There are two ways around this:

int? number = true ? (int?)5 : null;

Here we are still in the case where only one of x and y has a type. Note that null still does not have a type yet the compiler won't have any problem with this because (int?)5 and null are both implicitly convertible to int? (§6.1.4 and §6.1.5).

The other way is obviously:

int? number = true ? 5 : (int?)null;

but now we have to read a different clause in the spec to understand why this is okay:

If x has type X and y has type Y then

• If an implicit conversion (§6.1) exists from X to Y, but not from Y to X, then Y is the type of the conditional expression.

• If an implicit conversion (§6.1) exists from Y to X, but not from X to Y, then X is the type of the conditional expression.

• Otherwise, no expression type can be determined, and a compile-time error occurs.

Here x is of type int and y is of type int?. There is no implicit conversion from int? to int, but there is an implicit conversion from int to int? so the type of the expression is int?.

¹: Note further that the type of the left-hand side is ignored in determining the type of the conditional expression, a common source of confusion here.

No implicit conversion between int and null

null does not have any identifiable type - it just needs a little prodding to make it happy: Example is shown below.

int? number = true ? 5 : (int?)null;

Or you can do

int? number = true ? 5 : null as int?;

Type of conditional expression cannot be determined because there is no implicit conversion between 'int' and 'string'

Type of conditional expression cannot be determined because there is no implicit conversion between 'int' and 'string'

This means that return type of !Versioned.IsNumeric(text2)) ? -1 : text2 can't be narrowed to single type. It is either int (-1) or string (text2).

Treat both as string

int num = Conversions.ToInteger((!Versioned.IsNumeric(text2)) ? "-1" : text2);

Now, in either case the result of the conditional tenary operator will be string

Apply the condition outside

int num = Versioned.IsNumeric(text2) ? Conversions.ToInteger(text2) : -1;

• If text2 is numeric then convert string to int
• If text2 is not numeric then use -1

Type of conditional expression cannot be determined because there is no implicit conversion between System.DateTime and null

The issue is with the ternary operation. You're changing the data type from DateTime to a nullable DateTime. Ternary operations require you to return the same data type both before and after the colon. Doing something like this would work:

someDateTimeControl.Value = (tempDate > DateTime.MinValue) ? (DateTime?)tempDate : null;

Type of conditional expression cannot be determined because there is no implicit conversion between 'int?' and 'string'

Ternary operator expects both outputs to be of same type. Use the following:

Ages = m.RelatedMultipleWorks.Count == 0 ? m.RelatedLook.Age.ToString(): m.RelatedLook.Age.ToString() + " | " + m.RelatedMultipleWorks.Select(z => z.RelatedLook.Age.ToString()).Aggregate((current, next) => current + " | " + next),

Type of conditional expression cannot be determined because there is no implicit conversion between 'int' and 'null'

it happens because compiler tries to evaluate the right hand side first.

int.Parse((e.Item.FindControl("BankName_dd") as DropDownList).SelectedValue) is int and not nullable so there is a mismatch between parameters i.e int and null

Even this would be fine if you do it. this now wakes the first parameter as nullable int

int? BankName_dd = int.Parse((e.Item.FindControl("BankName_dd") as DropDownList).SelectedValue) != -1 ? (int?)int.Parse((e.Item.FindControl("BankName_dd") as DropDownList).SelectedValue):null;

SO already answered Link

---

Related Topics