Chapter 3 : Selection Structure

Question 1

What is a control structure?

Answer 1

1. logical design that controls the order in which statements execute

Question 2

What is a sequence structure?

Answer 2

1. Set of statements that execute in the order that
   they appear

Question 3

What circumstances that lets decision structure execute statements execute its statements?

Answer 3

1. Certain condition exists

• Decision structure is also known as selection structure

Question 4

What type for expression on decision structure?

Answer 4

1. Boolean expression that can be evaluated as either true or false

Question 5

How to write if statements in C#?

Answer 5

if ( expression )
{
statements
statements
}

Question 6

List out all relational operator ( 6 )

Answer 6

1. >
2. <
3. > =
4. <=
5. ==
6. !=

Question 7

What is the format for if-else statement?

Answer 7

if ( expression )
{
statements
}
else
{
statements
}

Question 8

Format for Nested Decision Structures

Answer 8

if ( expression )
{
if ( expression )
{
statement
}
else
{
statement
}
}
else
{
statements
}

Question 9

Format for if-else-if statement

Answer 9

if ( expression )
{
}
else if ( expression )
{
}
else if ( expression )
{
}
else
{
}

Question 10

List out 3 logical operator

Answer 10

1. && ( And )
2. || ( Or )
3. ! ( Not )

• ! ( Not Operator )
  if ( ! ( temperature > 100 ) )
  {
  MessageBox.Show(“Ok”)
  }

Question 11

What does switch statement does?

Answer 11

1. Lets the value of a variable or an expression determine which path of execution the program will take

• It is a multiple-alternative decision structure
• It can be used as an alternative to an if-else-if statement

Question 12

Format for switch statement

Answer 12

switch (testExpression)
{
case value_1:
statements
break
case value_n:
statements
break
default:
statements
break
}

Question 13

What is a testExpression in switch statement?

Answer 13

1. Variable or an expression that given an integer, string, or bool value

• It cannot be floating-point or decimal value

Question 14

List out 3 methods for comparing strings

Answer 14

1. Use == operator
   string n_1 = “Mark”
   string n_2 = “Max”

if ( n_1 == n_2 )
{
}

2. Compare string variables with string literals
   if ( n_1 = “Max” )
   {
   }
3. Use String.Compare
   string n_1 = “Mark”
   string n_2 = “Max”

if ( String.Compare(name1,name2)==0 )
{
}

Question 15

List out the syntax for preventing data conversion exception

Answer 15

int.TryParse( string , out targetVariable )

• Examples
  
  • int.TryParse
  • double.TryParse
  • decimal.TryParse
• out keyword is required, it specifies that the targetVariable is an output variable

Question 16

What is input validation?

Answer 16

1. The process of inspecting data that has been entered into a program to make sure it is valid before it is used

if ( hours > 0 && hours <= 168 )
{
}
else
{
}

• TryParse methods check if the user enters the data, but it doesn’t check the integrity of the data

Question 17

What is the difference between Radio Buttons & Check Boxes?

Answer 17

1. Radio Buttons allow usrs to select one choice from several possible choices
2. Check boxes allows users to select multiple options

Question 18

By clicking on a radio button, the program automatically deselects any others, this is known as what?

Answer 18

1. Mutually exclusive selection

Question 19

What is the common properties for RadioButton ? ( 2 )

Answer 19

1. Text
   
   • Holds the text that is displayed next to the radio button
2. Checked
   
   • A boolean property that determines whether the control is selected or deselected

Question 20

How to determine whether a RadioButton is selected?

Answer 20

if ( choiceRadioButton.Checked ) {
}
else{
}

• Is Same As

if ( choiceRadioButton.Checked == true ) {
}
else{
}

Question 21

What is raised when a RadioButton or CheckBox control’s Checked property changes?

Answer 21

1. CheckedChanged event

• I can write codes to respond to the event
• I can click the control in the Designer to create an empty CheckedChanged event

private void yellowRadioButton_CheckedChanged(object sender, EventArgs e) { }

Question 22

What is a list box?

Answer 22

1. Display a list of items and allow the user to select an item from the list

Question 23

List out 4 commonly used properties for the List Box

Answer 23

1. Text
   
   • Gets or searches for the text of the currently selected item in the List Box
2. Items
   
   • Gets the items of the ListBox
3. SelectedItem
   
   • Get or sets the currently selected item in the ListBox
4. SelectedIndex
   
   • Gets or sets the zero-based index of the currently selected item in a ListBox

Question 24

What will occur when I try to get the value of a ListBox SelectedItem property when no item is selected?

Answer 24

1. Exception will occur

Question 25

What is the starting index for SelectedItem property?

Answer 25

1. 0

Question 26

What is the index for SelectedIndex when there is no item selected?

Answer 26

1. -1

• Selection Structure to check if user didn’t select anything
  if (fruitListBox.SelectedIndex != -1) { }