问题
I can't figure out how to use switches in combination with an enum. Could you please tell me what I'm doing wrong, and how to fix it? I have to use an enum to make a basic calculator.
public enum Operator
{
PLUS, MINUS, MULTIPLY, DIVIDE
}
public double Calculate(int left, int right, Operator op)
{
int i = (int) op;
switch(i)
{
case 0:
{
return left + right;
}
case 1:
{
return left - right;
}
case 2:
{
return left * right;
}
case 3:
{
return left / right;
}
default:
{
return 0.0;
}
}
}
The end result should be something like this:
Console.WriteLine("The sum of 5 and 5 is " + Calculate(5, 5, PLUS))
Output: The sum of 5 and 5 is 10
Could you guys please tell me how I'm messing up?
回答1:
You don't need to convert it
switch(op)
{
case Operator.PLUS:
{
// your code
// for plus operator
break;
}
case Operator.MULTIPLY:
{
// your code
// for MULTIPLY operator
break;
}
default: break;
}
By the way, use brackets
回答2:
The correct answer is already given, nevertheless here is the better way (than switch):
private Dictionary<Operator, Func<int, int, double>> operators =
new Dictionary<Operator, Func<int, int, double>>
{
{ Operator.PLUS, ( a, b ) => a + b },
{ Operator.MINUS, ( a, b ) => a - b },
{ Operator.MULTIPLY, ( a, b ) => a * b },
{ Operator.DIVIDE ( a, b ) => (double)a / b },
};
public double Calculate( int left, int right, Operator op )
{
return operators.ContainsKey( op ) ? operators[ op ]( left, right ) : 0.0;
}
回答3:
simply don't cast to int
switch(operator)
{
case Operator.Plus:
//todo
回答4:
Since C# 8.0 introduced a new switch expression for enums you can do it even more elegant:
public double Calculate(int left, int right, Operator op) =>
op switch
{
Operator.PLUS => left + right,
Operator.MINUS => left - right,
Operator.MULTIPLY => left * right,
Operator.DIVIDE => left / right,
_ => 0
}
Ref. https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8
回答5:
You should not cast to integer. And for the division, you need to cast left to double first, if not you will be doing an integer divide.
public enum Operator
{
PLUS, MINUS, MULTIPLY, DIVIDE
}
public double Calculate(int left, int right, Operator op)
{
double sum = 0.0;
switch(op)
{
case Operator.PLUS:
sum = left + right;
return sum;
case Operator.MINUS:
sum = left - right;
return sum;
case Operator.MULTIPLY:
sum = left * right;
return sum;
case Operator.DIVIDE:
sum = (double)left / right;
return sum;
default:
return sum;
}
return sum;
}
回答6:
public enum Operator
{
PLUS, MINUS, MULTIPLY, DIVIDE
}
public class Calc
{
public void Calculate(int left, int right, Operator op)
{
switch (op)
{
case Operator.DIVIDE:
//Divide
break;
case Operator.MINUS:
//Minus
break;
case Operator.MULTIPLY:
//...
break;
case Operator.PLUS:
//;;
break;
default:
throw new InvalidOperationException("Couldn't process operation: " + op);
}
}
}
回答7:
In case you don't want to use return statement for each case, try this:
Calculate(int left, int right, Operator op)
{
int result = 0;
switch(op)
{
case Operator.PLUS:
{
result = left + right;;
}
break;
....
}
return result;
}
回答8:
All the other answers are correct, but you also need to call your method correctly:
Calculate(5, 5, Operator.PLUS))
And since you use int for left and right, the result will be int as well (3/2 will result in 1). you could cast to double before calculating the result or modify your parameters to accept double
回答9:
Two things. First, you need to qualify the enum reference in your test - rather than "PLUS", it should be "Operator.PLUS". Second, this code would be a lot more readable if you used the enum member names rather than their integral values in the switch statement. I've updated your code:
public enum Operator
{
PLUS, MINUS, MULTIPLY, DIVIDE
}
public static double Calculate(int left, int right, Operator op)
{
switch (op)
{
default:
case Operator.PLUS:
return left + right;
case Operator.MINUS:
return left - right;
case Operator.MULTIPLY:
return left * right;
case Operator.DIVIDE:
return left / right;
}
}
Call this with:
Console.WriteLine("The sum of 5 and 5 is " + Calculate(5, 5, Operator.PLUS));
回答10:
Your code is fine. In case you're not sure how to use Calculate function, try
Calculate(5,5,(Operator)0); //this will add 5,5
Calculate(5,5,Operator.PLUS);// alternate
Default enum values start from 0 and increase by one for following elements, until you assign different values. Also you can do :
public enum Operator{PLUS=21,MINUS=345,MULTIPLY=98,DIVIDE=100};
回答11:
No need to convert. You can apply conditions on Enums inside a switch. Like so,
public enum Operator
{
PLUS,
MINUS,
MULTIPLY,
DIVIDE
}
public double Calculate(int left, int right, Operator op)
{
switch (op)
{
case Operator.PLUS: return left + right;
case Operator.MINUS: return left - right;
case Operator.MULTIPLY: return left * right;
case Operator.DIVIDE: return left / right;
default: return 0.0;
}
}
Then, call it like this:
Console.WriteLine("The sum of 5 and 5 is " + Calculate(5, 5, Operator.PLUS));
来源：https://stackoverflow.com/questions/15136134/c-sharp-how-to-use-enum-with-switch