The following XAML-code
<esri:FeatureLayer ID="MyFeatureLayer"
Url="http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/0"
Where="POP1990 > 100000" />
is equivalent to:
double number = 100000;
FeatureLayer l = new FeatureLayer()
{
ID = "MyFeatureLayer",
Url = "http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/0",
Where = string.Format("POP1990 > {0}", number)
};
MyMap.Layers.Add(l);
You can use string.Format() with a number argument.