C# Case problem (invalid expression term ,,:")

Question

This is a code of a simple calculator that I'm trying to write, but there seem to be a problem with the switch statment (Visual Studio state that ,,invalid expression term ,,:"" and I really don't know why, because the code seems good to me.I want to add some more code later, but I don't want to continue before I don't deal with this problem.

int x, y, sum;
char input;

do
{
Console.WriteLine("Enter a value for x:");
x = Convert.ToInt32(Console.ReadLine());

Console.WriteLine("Enter a value for y:");
y = Convert.ToInt32(Console.ReadLine());

Console.WriteLine("What do you want to do? Add, substract, multiply or divide?");
input = Convert.ToChar(Console.ReadLine());

switch (input)
{
case + :
sum = x + y;
break;
case - :
sum = x - y;
break;
case * :
sum = x * y;
break;
case '/':
sum = x / y;
break;
}

}
while (true);

Answer 1

for chars mention in single quotes..
'+'
'-'
'*'
'/'

Answer 2

Thanks, It works now :)

Answer 3

You're welcome...