2. Core C# Flashcards
What do statements end with?
Statements end in a semicolon (;) and can continue over multiple lines without needing a continuation character.
How do you join statements into blocks?
Statements can be joined into blocks using curly braces ({}).
How do you create a single line comment?
Single-line comments begin with two forward slash characters (//).
How are multiline comments created?
Multiline comments begin with a slash and an asterisk (/*) and end with the same combination reversed (*/).
Is C# case sensitive?
C# is case-sensitive. Variables named myVar and MyVar are two different variables.
What are top-level statements?
You can create simple applications without defining a namespace, declaring a class, and defining a Main method.
What are four ways of creating a string that says “Hello World”?
string s1 = new string("Hello, World!");
string s2 = "Hello, World!";
var s3 = "Hello, World!";
string s4 = new("Hello, World!");
Can the var keyword be used with members of types.
the var keyword cannot be used with members of types.
What is scope?
The scope of a variable is the region of code from which the variable can be accessed.
What is the scope of a field?
The entire class.
A field (also known as a member variable) of a class is in scope for as long as its containing class is in scope.
What is the scope of a local variable?
A local variable is in scope only within it’s block.
A local variable is in scope until a closing brace indicates the end of the block statement or method in which it was declared.
What is the scope of a variable in a loop?
The loop itself.
A local variable that is declared in a for, while, or similar statement is in scope in the body of that loop.
Can a variable with the same name be declared more than once within a single scope?
No.
However, bear in mind that local variables with the same name can’t be declared twice in the same scope.
How do you declare a variable that should never change?
Use the ‘const’ keyword.
For values that never change, you can define a constant. For constant values, you can use the const keyword.
What are three characteristics of constants?
- They must be initialized when they are declared.
- You can’t initialize a constant with a value taken from a variable.
- Constants are always implicitly static.
If a variable in different instances of a class or method can have different values, but once that variable is decided it will never change, should it be made into a constant?
No, make it readonly instead
Can you place top-level statements in any file?
No.
Can a value type such as int, float, or double be null?
Not normally. The ‘?’ operator has to used to make a value type capable of being null.
Can reference types, such as a string, be made null.
Yes.
A special effort is needed to make them not be nullable. This is the purpose of Nullable Reference Types.
Why can reference types with a null value be problematic?
If you try to perform an operation on a variable that has a null value, it will most often throw an exception.
What is the purpose of “nullable reference types”?
To reduce NullReferenceExceptions being thrown.
“Nullable reference types” has to be turned on and once it is the compiler will create an error if a reference value is null.
What is the null-conditional operator?
It is a way to check a reference for being null before invoking a method on it (If you do, and the reference variable is null, you will get a NullReferenceException).
The null-conditional operator is: .? (A period and a question mark.)
What is the coalescing operator?
It’s a way of defining a default return type is a reference variable is null. This operator is two question marks: ??
When you declare an ‘int’ in C#, what are you actually doing?
You are actually declaring a ‘System.Int32”.
What are the built-in value types?
- integers
- floating-point numbers (float, double, decimal)
- characters
- Booleans
What are the 8-bit integer types?
- byte (can only have a positive value, unsigned)
- sbyte (can have negative and positive values)
What are the 16-bit integer types?
- short
- ushort (unsigned)
What are the 32-bit integer types?
- int
- uint (unsigned)
What are the 64-bit integer types?
- long
- ulong (unsigned)
How do check an integer types maximum and minimum values?
Use one these properties:
- MaxValue
- MinValue
Example:
Console.WriteLine(int.MaxValue);
What are digit separators?
They are a way to make numbers easier to read. The ‘_’ operator.
In C# the number
10000000000
is equvilante to
10_000_000_000
What is a floating-point type?
It is a number that that has decimals. Unlike integers which cannot support decimals.
What are the four types of floating-point numbers?
- System.Half
- float
- double
- decimal
Which floating point type can be used with money transactions?
The decimal type.
How many built-in reference types are there?
Two
- object
- string
What are the four general-purpose methods created by the object type?
- Equals
- GetHashCode
- GetType
- ToString
What’s the difference in the programming flow created by the ‘if’ and ‘switch’ statement versus the loop statements, ‘for’, ‘while’, ‘do-while’, ‘foreach’.
‘if’ and ‘switch’ will branch you program.
The loops will repeat statements until a condition is met.
What are the three keywords associated with the ‘if’ statement?
- if
- else if
- else
How do you use the const pattern with the ‘is’ statement? (Using an ‘if’ statement).
This compares one item with a constant to determine if they are similar.
How do you use the type pattern with the ‘is’ statement? (Using an ‘if’ statement).
Here an object is being asked if it is a certain Type, if it is it evaluates to true.
Which is a switch statement?
Performs the same function as an ‘if’ statement, but the switch has more flexability. Also, you do not need to use as many curly braces.
What are the six important keywords and operators associated with switch statements.
- switch
- case
- default
- when
- break
- : (the colon)
How do you use the constant pattern with the switch statement?
This is so easy that giving it a name makes it seem harder.
Basically, if the object has the value of the constant, then that is the case that is chosen.
How do you use the type pattern with the switch statement?
If the object is the same type as the type being asked for, that case will be selected.
How is the relational pattern used with the switch statement?
The ‘when’ keyword used with a type pattern is the relational pattern.
First, this pattern looks for a specific type, but also constrains that type to be a certain value or range of values.
Are the switch statement and switch expression the same thing?
No, they are two different ways of using the switch statement, but they do perform a similar function.
The biggest obvious difference is that the switch statement uses the ‘case’ keyword, while the switch expression does not, but uses “ => “ instead.
With regard to switch expressions, what are the pattern combinators.
They are the ‘and’, ‘or’, and ‘not’ keywords.
You use them just as you would to create a compound conditional if statement
What are the four loop types?
for, while, do - while, and foreach.
What are the three parts of a for loop?
The initializer, the condition, and the iterator.
What is a ‘while’ loop?
A while loop continues while a specified condition is true. When the condition is changed to false the loop stops.
Basic format:
while(condition is true)
statement(s);
What is the do-while loop?
The do-while loop is an upside down version of the do loop.
It has this format:
do
{
statement(s);
}while(condition)
What is a ‘foreach loop’?
A ‘foreach loop’ will allow you to step throw a collection of objects (basically a list of items) then do something with each item in that collection.
List the keywords associated with a foreach loop.
- foreach
- in
Other than reaching the conditions set in a loop, what are three other ways of stopping an iteration.
- break (this will end the loop)
- coninue (this will not end the loop but go back to the top of the loop)
- return (this will exit a method that is in the loop and exit the loop)
What are the purpose of namespaces?
To prevent conflicts between classes that might have the same name. The namespace that the class is associated with is part of that class full name.
Can a string type be changed?
No, strings are immutable.
However, this is mostly not noticeable, especially for small strings, because if a string is changed, .net will delete the old one and create a new without you even realizing it. If the strings become very large though, this will become probamatic.
What is string concatenation?
It is when two strings are added together?
What is StringBuilder?
StringBuilder is an alternative to the string type. It allows you to work with strings without creating an new object every time the string is changed.
What is string interpolation?
It allows you to insert a variable into the body of the string.
What are the important operators associated with string interpolation?
- $ (The dollar sign)
- { } (the two squiggly brackets)
What is a verbatim string? What is the verbatim symbol?
The verbatim symbol is @.
A verbatim string returns the string just as it is between the two quotes, “”.
What are the operators for the single and multiple line comments?
// (Two slashes for the single line comment)
/* a bunc of words */ (Start the comment with a slash/asterisk, add your comments, then end with asterisk/slash).
What is XML documentation?
It’s a way to document and clutter-up your code while you are in the very act of writing the code. It uses three of the slashes ( /// ).
What is nice about xml documentation are that these comments will show up in intellisense.
What’s the rule for beginning an identifier?
An identifier (also called a name) must start with a letter or underscore.
So yourName and _yourName are both valid names
But 2yourName and @yourName are not valid
What is the rule concerning identifiers and keywords?
You can’t use keywords as identifiers.
The exception being if you prefex the keyword with the @ symbol
What should your identifiers reflect?
They should reflect the underlining purpose of the identifier?
Are there many conventions (general agreed on ways of doing things) in c# which does not hinder the running of the code if not follow, but if not followed will make it harder for others to read your code.
Yes, of course there are. More rules.
But they are rules designed to make the code easier to read, which is a good thing.
What is Pascal casing and when should you use it for your names?
Pascal casing is the capitalizing the first letter of each word that makes up a name.
When should Pascal casing be used for a name?
The major parts of your code should use Pascal casing, such as namespaces, classes, methods, etc.
Should the _ (underscore) be used to join words in an identifier.
No.
Use Pascal casing instead.
What is camel casing and when should it be used?
Camel casing is a bit like Pascal casing except the first letter of the indentifier is lower case.
It should be used for:
- private fields
- parameters passed to methods
- Items that otherwise have the same name
When should you use a property?
If the item should look and behave like a variable.
Should a field be public or private.
Almost always private.
