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| // String.Concat example. | |
| // String.Concat has many versions. Rest the mouse pointer on | |
| // Concat in the following statement to verify that the version | |
| // that is used here takes three object arguments. Both 42 and | |
| // true must be boxed. | |
| Console.WriteLine(String.Concat("Answer", 42, true)); | |
| // List example. | |
| // Create a list of objects to hold a heterogeneous collection | |
| // of elements. | |
| List<object> mixedList = new List<object>(); | |
| // Add a string element to the list. | |
| mixedList.Add("First Group:"); | |
| // Add some integers to the list. | |
| for (int j = 1; j < 5; j++) | |
| { | |
| // Rest the mouse pointer over j to verify that you are adding | |
| // an int to a list of objects. Each element j is boxed when | |
| // you add j to mixedList. | |
| mixedList.Add(j); | |
| } | |
| // Add another string and more integers. | |
| mixedList.Add("Second Group:"); | |
| for (int j = 5; j < 10; j++) | |
| { | |
| mixedList.Add(j); | |
| } | |
| // Display the elements in the list. Declare the loop variable by | |
| // using var, so that the compiler assigns its type. | |
| foreach (var item in mixedList) | |
| { | |
| // Rest the mouse pointer over item to verify that the elements | |
| // of mixedList are objects. | |
| Console.WriteLine(item); | |
| } | |
| // The following loop sums the squares of the first group of boxed | |
| // integers in mixedList. The list elements are objects, and cannot | |
| // be multiplied or added to the sum until they are unboxed. The | |
| // unboxing must be done explicitly. | |
| var sum = 0; | |
| for (var j = 1; j < 5; j++) | |
| { | |
| // The following statement causes a compiler error: Operator | |
| // '*' cannot be applied to operands of type 'object' and | |
| // 'object'. | |
| //sum += mixedList[j] * mixedList[j]); | |
| // After the list elements are unboxed, the computation does | |
| // not cause a compiler error. | |
| sum += (int)mixedList[j] * (int)mixedList[j]; | |
| } | |
| // The sum displayed is 30, the sum of 1 + 4 + 9 + 16. | |
| Console.WriteLine("Sum: " + sum); | |
| // Output: | |
| // Answer42True | |
| // First Group: | |
| // 1 | |
| // 2 | |
| // 3 | |
| // 4 | |
| // Second Group: | |
| // 5 | |
| // 6 | |
| // 7 | |
| // 8 | |
| // 9 | |
| // Sum: 30 |