H4-Using Types

Question 1

what is the “is” operator

Answer 1

check if instance is of certain type. if (user is Employee)…

Question 2

what is the “as” operator

Answer 2

check if instance is of type otherwise result null.

Employee emp = user as Employee;
if (emp != null)
{…

Question 3

how can you use “as” to do a cast?

Answer 3

RadioButton rad = sender as RadioButton;

Question 4

How to cast child array to parent array

Answer 4

parentArrayType MyRef = childArrayInstance

Question 5

cast back parentarray to childarray 3 examples

Answer 5

ChildArryType MyRef = (ParentArrayType) instance;
if(instance is ChildArryType) {…
MyRef = instance as ChildArryType

Question 6

How copy an array

Answer 6

Array.Copy(

Question 7

How to convert a value to/from an array of bytes

Answer 7

BitConverter.GetBytes or BitConverter.ToInt..

Question 8

How can you force an exception beeing thrown when casting to an int (under/overflow)

Answer 8

checked
{
int big = 1000000;
short small = (short)big;
}

Question 9

what is a risk when using “checked”

Answer 9

only direct code is checked, if a methode is called in the checked body then no check is done inside the methode.

Question 10

do you get an exception when you get an overflow/underflow on an int type?

Answer 10

No, application keeps running, so alway check this using the “checked” body.

Question 11

do you get an exception when you get an overflow/underflow on an float type?

Answer 11

No, float goes to infinity, this can be checked with float.IsInfinity(floatInstanceUsed)

Question 12

How can you parse a string to an int when not using a try/catch block?

Answer 12

int.TryParse(weightTextBox.Text, out weight)

Note: out is a ref to the output var, in this case weight.

Question 13

How can you alter the allowed parsing text. e.g.int.Parse(“$1000,00”)

Answer 13

Use System.Globalization.NumberStyles
example :

decimal amount = decimal.Parse(“$123,456.78”,
NumberStyles.AllowCurrencySymbol |
NumberStyles.AllowThousands |
NumberStyles.AllowDecimalPoint);

Question 14

what is : banker’s rounding?

Answer 14

means values are rounded to the nearest integer, but if
there’s a tie, with the value ending in exactly .5, the value is rounded to the nearest
even integer.

Question 15

which rounding type does the “Math.Round” use?

Answer 15

banker’s rounding

Question 16

what can go wrong when you box a valuetype

Answer 16

the boxes valuetype does not point to the valuetype, therefore if you change the valuetype the boxed type does not change.

Question 17

What is an “intern pool”

Answer 17

Location where all strings are stored. Multiple refs with same string value point to the same string location, so there is only one of each kind/value.

Question 18

How can you create an empty string

Answer 18

String.Empty

Question 19

what is a dynamic type?

Answer 19

Type that does not get evaluated during compilation.

// Make an array of numbers.
int[] array1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
// This doesn't work because array1.Clone is an object.
//int[] array2 = array1.Clone();
// This works.
int[] array3 = (int[])array1.Clone();
array3[5] = 55;
// This also works.
dynamic array4 = array1.Clone();
array4[6] = 66;
array4[7] = "This won't work";

Question 20

How to check if a string is empty.

Answer 20

String.IsNullOrEmpty String.Empty

StringRef = String.Empty;

Question 21

give an example of a string.format

Answer 21

{index[,length][:formatString]}

The format string is {0} = {1,4} or 0x{2:X}. This string has three format items that mean:

• {0} displays argument 0 with default formatting
• {1,4} displays argument 1 in a field at least four characters wide
• {2:X} displays argument 2 with format string X (which displays an integer in hexadecimal)