If-statement GetType() c#

if (numerator is int) { ... }

or

if (numerator.GetType() == typeof(int)) {...}

The former is usually better.

EDIT: Нou say the problem is parsing numbers from string representation. I'm afraid, the best approach here is to call type.TryParse and check if given string can be parsed as a number of given type.

E.g.

var tokens = line.Split('/');
double dArg1,dArg2; int iArg1, iArg2;
if (int.TryParse(tokens[0], out iArg1) 
    && int.TryParse(tokens[1], out iArg2)){
    return iArg1/iArg2;
} else if (double.TryParse(tokens[0], out dArg1) 
           && double.TryParse(tokens[1], out dArg2)){
    return dArg1/dArg2;
} else { /* handle error */ }

Note that all ints can be parsed as doubles, so you need to try to parse token as int before trying to parse it as `double.

if (numerator.GetType() == typeof(int))
{
    ...
}

typeof (MSDN)

You can use the typeof-operator:

if(typeof(int) == numerator.GetType())
{
    //put code here
}