Array.IndexOf(T) Method (T, T)
Searches for the specified object and returns the index of the first occurrence within the entire Array.
Assembly: mscorlib (in mscorlib.dll)
The type of the elements of the array.
- Type: 
The one-dimensional, zero-based Array to search.
The object to locate in array.
Return ValueType: System.Int32
The zero-based index of the first occurrence of value within the entire array, if found; otherwise, –1.
array is a null reference (Nothing in Visual Basic).
The Array is searched forward starting at the first element and ending at the last element.
The elements are compared to the specified value using the Object.Equals method. If the element type is a nonintrinsic (user-defined) type, the Equals implementation of that type is used.
This method is an O(n) operation, where n is the Length of array.
The following code example demonstrates all three generic overloads of the IndexOf method. An array of strings is created, with one entry that appears twice, at index location 0 and index location 5. The method overload searches the array from the beginning, and finds the first occurrence of the string. The IndexOf(T)(T, T, Int32) method overload is used to search the array beginning with index location 3 and continuing to the end of the array, and finds the second occurrence of the string. Finally, the IndexOf(T)(T, T, Int32, Int32) method overload is used to search a range of two entries, beginning at index location two; it returns –1 because there are no instances of the search string in that range.
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2