So disclaimer, I am pretty new to C# and trying to learn the finer intricacies. I have a classwork assignment that I coded and it works, but I'm not sure why it works, and want to understand it.
Here is the code, Its not the full code, i just cut out the relevant parts:
int studentType = 0;
switch (studentType)
{
case 1:
studentType = '1';
WriteLine("What is your GPA?");
gpa = Convert.ToDouble(ReadLine());
break;
case 2:
studentType = '2';
WriteLine("What is the title of your thesis?");
thesis = ReadLine();
break;
case 3:
studentType = '3';
WriteLine("What is the title of your dissertation?");
dissertation = ReadLine();
break;
case 4:
break;
default:
WriteLine("Invalid option input.");
break;
}//Switch for student Type
As noted, the case command works perfectly fine like this. What I accidently did was initially put case 'x': and that ended up not working, so i deleted all the single quotes.
Here is the 2nd part, and why I am confused:
switch (studentType)
{
case '1':
case '4':
WriteLine($"GPA: {gpa:f2}");
break;
case '3':
WriteLine($"Dissertation title: {dissertation}");
break;
case '2':
WriteLine($"Thesis title: {thesis}");
break;
}//end of studentType switch
So originally I tried writing the case without the single quotes, but every time I ran 1, GPA never populated, so I tried to put in the single quotes, and it works, but I'm not sure why.
Since studentType is an integer, it would make sense for the first switch to be without single quotes, but how is the switch requiring single quotes?
I guess I can submit it as is as long as it works correctly, but I mainly want to understand whats going on.
Thanks for the help!
There's an implicit conversion from char to int, and a constant char expression can be used as a constant int expression, which is what you've got. The value of the int is the UTF-16 code unit associated with the char.
Here's another example of that:
const int X = 'x';
That's also why your assignment statements worked:
studentType = '1';
So this:
int value = ...;
switch (value)
{
case '1':
// ...
break;
}
is equivalent to:
int value = ...;
switch (value)
{
case 49:
// ...
break;
}
... because 49 is the UTF-16 code point associated with the character '1'.
So I have a task from a worksheet at work:
I have to change these Ifs to a switch, but how do i do it? Heres the Ifs:
if (i<0 || i>15) Console.WriteLine ("A");
else if (i%5<2 && i/3>3) Console.WriteLine ("B");
else if (3<i && i<10) Console.WriteLine ("C");
else if (i&2==2) Console.WriteLine ("D");
else Console.WriteLine ("E");
and here is the switch i made, but that one is bad, but i dont know how to make a good one out of it, i hope you can help me with this.
switch (i)
case (i<0):
case (i>15):
Console.WriteLine ("A“)
Break;
Case (i%5<2 && i/3>3) :
Console.WriteLine ("B“)
Break;
case (3<i && i<10) :
Console.WriteLine ("C");
Break;
Case (i&2==2) :
Console.WriteLine ("D");
Break;
Default
Console.WriteLine ("E");
Break;
It doesnt have to run in a programm, it's just a task from a worksheet
I haven't figured out all the rules completely, but I think what you're after is something like this:
The question wants you to realise that you've got a limited number of results, since the first rule is (i<0 || i>15). This can be the default for a switch statement.
Then you need to work out what would happen for all integers 0-15 and write them into the rest of the switch.
So you're after something along the lines of (although this doesn't have your logic - you can figure that out so you understand what's going on):
switch (i)
{
case 0:
case 2:
case 5:
Console.Write("Something")
break;
case 1:
case 7:
Console.Write("Something Else")
break;
default
Console.WriteLine ("A“)
Break;
}
I think it's:
switch (i)
{
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
Console.WriteLine("C");
break;
case 0:
case 1:
case 3:
case 10:
case 11:
case 12:
case 13:
case 14:
Console.WriteLine("E");
break;
case 2:
Console.WriteLine("D");
break;
case 15:
Console.WriteLine("B");
break;
default:
Console.WriteLine("A");
break;
}
Use a separate variable, in which you have to embed the segmentation logic. Here is a sample:
//using enum
public enum MySwitchableVariable {
NotDefined, //optional
LessThanZero,
MoreThanFifteen,
RestOfFiveLessThanTwoAndFactorMoreThanThree, //its too complex to describe
BetweenThreeAndTen,
RestOfTwoIsTwo,
}
Then you have to make a function which takes an integer and spit out a case of this enum:
public MySwitchableVariable calculate(int i) {
var result = MySwitchableVariable.NotDefined;
// your implementation here
return result;
}
finally you may switch that annoying variable like this:
var Variable = calculate(i);
switch(Variable) {
case MySwitchableVariable.LessThanZero:
// you know the rest
is that what you (or your instructor) want?
Simply you can't do this. Using the switch statement entails that the variable in switch can take a number of discrete constant values.
From the documentation:
The switch statement is a control statement that selects a switch
section to execute from a list of candidates.
Furthermore,
Each case label specifies a constant value. The switch statement transfers control to the switch section whose case label matches the
value of the switch expression (caseSwitch in the example). If no case
label contains a matching value, control is transferred to the default
section, if there is one. If there is no default section, no action is
taken and control is transferred outside the switch statement. In the
previous example, the statements in the first switch section are
executed because case 1 matches the value of caseSwitch.
This question already has answers here:
Multiple cases in switch statement
(24 answers)
Switch case: can I use a range instead of a one number [duplicate]
(16 answers)
Closed 1 year ago.
Does anyone know if it's possible to include a range in a switch statement (and if so, how)?
For example:
switch (x)
{
case 1:
//do something
break;
case 2..8:
//do something else
break;
default:
break;
}
The compiler doesn't seem to like this kind of syntax - neither does it like:
case <= 8:
No, this isn't possible. There are a few ways I've done this in the past:
Fixed coding:
switch (x)
{
case 1:
//do something
break;
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
//do something else
break;
default:
break;
}
In combination with an if {} statement:
switch (x)
{
case 1:
//do something
break;
default:
if (x <= 8)
{
// do something
}
else
{
// throw exception
}
break;
}
No, but you can write this, so you at least avoid writing the // do something else part multiple times.
switch (x)
{
case 1:
//do something
break;
case 2: case 3: case 4: case 5: case 6: case 7: case 8:
//do something else
break;
default:
break;
}
Whilst this wasn't possible when I originally asked this question, through the miracle of C# Pattern Matching, it now is (in C# 7):
switch (i)
{
case var test when test <= 2:
Console.WriteLine("Less than 2");
break;
case var test when test > 2 && test < 10:
Console.WriteLine("Between 2 and 10");
break;
case var test when test >= 10:
Console.WriteLine("10 or more");
break;
}
A blog post on the subject
Short answer : no. It would be possible to write all of the cases there but such a range notation is not supported.
I think you have to use if statement here or switch to a language where there is a better support for case descrimination.
One possibility is to convert your ranges into integers. For example:
//assuming x>=9 or if (x <= 0) return;
switch((x+12)/7)
{ case 1:Console.WriteLine("one");
break;
case 2:Console.WriteLine("2 through 8 inclusive");
break;
case 3:Console.WriteLine("9 through 15 inclusive");
break;
default: Console.WriteLine("16 or more");
break;
}
If you have so few cases, if would be much preferred.
You could, handle the explicit cases case by case, and if you only have one range, deal with it in the default case.
you can do
case 2:
case 3:
case 4:
...
case 8:
// code here
break
You can use case fall through:
switch (x)
{
case 1:
//do something
break;
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
//do something else
break;
default:
break;
}
But I'd just use if for this.
You cannot use any conditional statements in a switch case.
If you want to execute the same lines of code for different options then you can do one thing:
switch (i)
{
case 0:
case 1:
case 2:
case 3:
//do something here.
break;
default:
//do something here.
break;
}
It appears I need to use a break in each case block in my switch statement using C#.
I can see the reason for this in other languages where you can fall through to the next case statement.
Is it possible for case blocks to fall through to other case blocks?
Thanks very much, really appreciated!
Yes, you can fall through to the next case block in two ways. You can use empty cases, which don't need a break, or you can use goto to jump to the next (or any) case:
switch (n) {
case 1:
case 2:
case 3:
Console.WriteLine("1, 2 or 3");
goto case 4;
case 4:
Console.WriteLine(4);
break;
}
The enforcement of "break" is there to stop bugs. If you need to force a fall-thru then use "goto case " (replace the with appropriate value)
the following example shows what you can do:
switch(n)
{
case 1:
case 2:
//do something for 1+2
//...
goto case 3;
case 3:
//do something for 3, and also extra for 1+2
//...
break;
default:
//do something for all other values
//...
break;
}
See http://msdn.microsoft.com/en-us/library/06tc147t%28VS.80%29.aspx
C# doesn't support implicit fall through construct, but the break (or goto) nonetheless has to be there (msdn). The only thing you can do is stack cases in the following manner:
switch(something) {
case 1:
case 2:
//do something
break;
case 3:
//do something else
}
but that break (or another jump statement like goto) just needs to be there.
In my C# (.NET 1.1, CF) code, both of these are allowed:
switch (_printerChoice)
{
case BeltPrintersEnum.ZebraQL220:
return new ZebraQL220Printer();
break;
case BeltPrintersEnum.ONeal:
return new ONealPrinter();
break;
default:
return new ZebraQL220Printer();
break;
}
switch (_printerChoice)
{
case BeltPrintersEnum.ZebraQL220:
return new ZebraQL220Printer();
case BeltPrintersEnum.ONeal:
return new ONealPrinter();
default:
return new ZebraQL220Printer();
}
...but with the breaks in, they are grayed out, so considered moot. So, at least in my case, they are allowed but not required.
Is there a way to fall through multiple case statements without stating case value: repeatedly?
I know this works:
switch (value)
{
case 1:
case 2:
case 3:
// Do some stuff
break;
case 4:
case 5:
case 6:
// Do some different stuff
break;
default:
// Default stuff
break;
}
but I'd like to do something like this:
switch (value)
{
case 1,2,3:
// Do something
break;
case 4,5,6:
// Do something
break;
default:
// Do the Default
break;
}
Is this syntax I'm thinking of from a different language, or am I missing something?
I guess this has been already answered. However, I think that you can still mix both options in a syntactically better way by doing:
switch (value)
{
case 1: case 2: case 3:
// Do Something
break;
case 4: case 5: case 6:
// Do Something
break;
default:
// Do Something
break;
}
There is no syntax in C++ nor C# for the second method you mentioned.
There's nothing wrong with your first method. If however you have very big ranges, just use a series of if statements.
Original Answer for C# 7
In C# 7 (available by default in Visual Studio 2017/.NET Framework 4.6.2), range-based switching is now possible with the switch statement and would help with the OP's problem.
Example:
int i = 5;
switch (i)
{
case int n when (n >= 7):
Console.WriteLine($"I am 7 or above: {n}");
break;
case int n when (n >= 4 && n <= 6 ):
Console.WriteLine($"I am between 4 and 6: {n}");
break;
case int n when (n <= 3):
Console.WriteLine($"I am 3 or less: {n}");
break;
}
// Output: I am between 4 and 6: 5
Notes:
The parentheses ( and ) are not required in the when condition, but are used in this example to highlight the comparison(s).
var may also be used in lieu of int. For example: case var n when n >= 7:.
Updated examples for C# 9
switch(myValue)
{
case <= 0:
Console.WriteLine("Less than or equal to 0");
break;
case > 0 and <= 10:
Console.WriteLine("More than 0 but less than or equal to 10");
break;
default:
Console.WriteLine("More than 10");
break;
}
or
var message = myValue switch
{
<= 0 => "Less than or equal to 0",
> 0 and <= 10 => "More than 0 but less than or equal to 10",
_ => "More than 10"
};
Console.WriteLine(message);
This syntax is from the Visual Basic Select...Case Statement:
Dim number As Integer = 8
Select Case number
Case 1 To 5
Debug.WriteLine("Between 1 and 5, inclusive")
' The following is the only Case clause that evaluates to True.
Case 6, 7, 8
Debug.WriteLine("Between 6 and 8, inclusive")
Case Is < 1
Debug.WriteLine("Equal to 9 or 10")
Case Else
Debug.WriteLine("Not between 1 and 10, inclusive")
End Select
You cannot use this syntax in C#. Instead, you must use the syntax from your first example.
With C#9 came the Relational Pattern Matching. This allows us to do:
switch (value)
{
case 1 or 2 or 3:
// Do stuff
break;
case 4 or 5 or 6:
// Do stuff
break;
default:
// Do stuff
break;
}
In deep tutorial of Relational Patter in C#9
Pattern-matching changes for C# 9.0
Relational patterns permit the programmer to express that an input
value must satisfy a relational constraint when compared to a constant
value
You can leave out the newline which gives you:
case 1: case 2: case 3:
break;
but I consider that bad style.
.NET Framework 3.5 has got ranges:
Enumerable.Range from MSDN
you can use it with "contains" and the IF statement, since like someone said the SWITCH statement uses the "==" operator.
Here an example:
int c = 2;
if(Enumerable.Range(0,10).Contains(c))
DoThing();
else if(Enumerable.Range(11,20).Contains(c))
DoAnotherThing();
But I think we can have more fun: since you won't need the return values and this action doesn't take parameters, you can easily use actions!
public static void MySwitchWithEnumerable(int switchcase, int startNumber, int endNumber, Action action)
{
if(Enumerable.Range(startNumber, endNumber).Contains(switchcase))
action();
}
The old example with this new method:
MySwitchWithEnumerable(c, 0, 10, DoThing);
MySwitchWithEnumerable(c, 10, 20, DoAnotherThing);
Since you are passing actions, not values, you should omit the parenthesis, it's very important. If you need function with arguments, just change the type of Action to Action<ParameterType>. If you need return values, use Func<ParameterType, ReturnType>.
In C# 3.0 there is no easy Partial Application to encapsulate the fact the the case parameter is the same, but you create a little helper method (a bit verbose, tho).
public static void MySwitchWithEnumerable(int startNumber, int endNumber, Action action){
MySwitchWithEnumerable(3, startNumber, endNumber, action);
}
Here an example of how new functional imported statement are IMHO more powerful and elegant than the old imperative one.
Here is the complete C# 7 solution...
switch (value)
{
case var s when new[] { 1,2,3 }.Contains(s):
// Do something
break;
case var s when new[] { 4,5,6 }.Contains(s):
// Do something
break;
default:
// Do the default
break;
}
It works with strings too...
switch (mystring)
{
case var s when new[] { "Alpha","Beta","Gamma" }.Contains(s):
// Do something
break;
...
}
The code below won't work:
case 1 | 3 | 5:
// Not working do something
The only way to do this is:
case 1: case 2: case 3:
// Do something
break;
The code you are looking for works in Visual Basic where you easily can put in ranges... in the none option of the switch statement or if else blocks convenient, I'd suggest to, at very extreme point, make .dll with Visual Basic and import back to your C# project.
Note: the switch equivalent in Visual Basic is Select Case.
Another option would be to use a routine. If cases 1-3 all execute the same logic then wrap that logic in a routine and call it for each case. I know this doesn't actually get rid of the case statements, but it does implement good style and keep maintenance to a minimum.....
[Edit] Added alternate implementation to match original question...[/Edit]
switch (x)
{
case 1:
DoSomething();
break;
case 2:
DoSomething();
break;
case 3:
DoSomething();
break;
...
}
private void DoSomething()
{
...
}
Alt
switch (x)
{
case 1:
case 2:
case 3:
DoSomething();
break;
...
}
private void DoSomething()
{
...
}
In C# 7 we now have Pattern Matching so you can do something like:
switch (age)
{
case 50:
ageBlock = "the big five-oh";
break;
case var testAge when (new List<int>()
{ 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 }).Contains(testAge):
ageBlock = "octogenarian";
break;
case var testAge when ((testAge >= 90) & (testAge <= 99)):
ageBlock = "nonagenarian";
break;
case var testAge when (testAge >= 100):
ageBlock = "centenarian";
break;
default:
ageBlock = "just old";
break;
}
One lesser known facet of switch in C# is that it relies on the operator= and since it can be overriden you could have something like this:
string s = foo();
switch (s) {
case "abc": /*...*/ break;
case "def": /*...*/ break;
}
gcc implements an extension to the C language to support sequential ranges:
switch (value)
{
case 1...3:
//Do Something
break;
case 4...6:
//Do Something
break;
default:
//Do the Default
break;
}
Edit: Just noticed the C# tag on the question, so presumably a gcc answer doesn't help.
I think this one is better in C# 7 or above.
switch (value)
{
case var s when new[] { 1,2 }.Contains(s):
// Do something
break;
default:
// Do the default
break;
}
You can also check Range in C# switch case: Switch case: can I use a range instead of a one number
OR
int i = 3;
switch (i)
{
case int n when (n >= 7):
Console.WriteLine($"I am 7 or above: {n}");
break;
case int n when (n >= 4 && n <= 6):
Console.WriteLine($"I am between 4 and 6: {n}");
break;
case int n when (n <= 3):
Console.WriteLine($"I am 3 or less: {n}");
break;
}
Switch case multiple conditions in C#
Or if you want to understand basics of
C# switch case
Actually I don't like the GOTO command too, but it's in official Microsoft materials, and here are all allowed syntaxes.
If the end point of the statement list of a switch section is reachable, a compile-time error occurs. This is known as the "no fall through" rule. The example
switch (i) {
case 0:
CaseZero();
break;
case 1:
CaseOne();
break;
default:
CaseOthers();
break;
}
is valid because no switch section has a reachable end point. Unlike C and C++, execution of a switch section is not permitted to "fall through" to the next switch section, and the example
switch (i) {
case 0:
CaseZero();
case 1:
CaseZeroOrOne();
default:
CaseAny();
}
results in a compile-time error. When execution of a switch section is to be followed by execution of another switch section, an explicit goto case or goto default statement must be used:
switch (i) {
case 0:
CaseZero();
goto case 1;
case 1:
CaseZeroOrOne();
goto default;
default:
CaseAny();
break;
}
Multiple labels are permitted in a switch-section. The example
switch (i) {
case 0:
CaseZero();
break;
case 1:
CaseOne();
break;
case 2:
default:
CaseTwo();
break;
}
I believe in this particular case, the GOTO can be used, and it's actually the only way to fallthrough.
Source
In C# 8.0 you can use the new switch expression syntax which is ideal for your case.
var someOutput = value switch
{
>= 1 and <= 3 => <Do some stuff>,
>= 4 and <= 6 => <Do some different stuff>,
_ => <Default stuff>
};
If you have a very big amount of strings (or any other type) case all doing the same thing, I recommend the use of a string list combined with the string.Contains property.
So if you have a big switch statement like so:
switch (stringValue)
{
case "cat":
case "dog":
case "string3":
...
case "+1000 more string": // Too many string to write a case for all!
// Do something;
case "a lonely case"
// Do something else;
.
.
.
}
You might want to replace it with an if statement like this:
// Define all the similar "case" string in a List
List<string> listString = new List<string>(){ "cat", "dog", "string3", "+1000 more string"};
// Use string.Contains to find what you are looking for
if (listString.Contains(stringValue))
{
// Do something;
}
else
{
// Then go back to a switch statement inside the else for the remaining cases if you really need to
}
This scale well for any number of string cases.
You can also have conditions that are completely different
bool isTrue = true;
switch (isTrue)
{
case bool ifTrue when (ex.Message.Contains("not found")):
case bool ifTrue when (thing.number = 123):
case bool ifTrue when (thing.othernumber != 456):
response.respCode = 5010;
break;
case bool ifTrue when (otherthing.text = "something else"):
response.respCode = 5020;
break;
default:
response.respCode = 5000;
break;
}
An awful lot of work seems to have been put into finding ways to get one of C# least used syntaxes to somehow look better or work better. Personally I find the switch statement is seldom worth using. I would strongly suggest analyzing what data you are testing and the end results you are wanting.
Let us say for example you want to quickly test values in a known range to see if they are prime numbers. You want to avoid having your code do the wasteful calculations and you can find a list of primes in the range you want online. You could use a massive switch statement to compare each value to known prime numbers.
Or you could just create an array map of primes and get immediate results:
bool[] Primes = new bool[] {
false, false, true, true, false, true, false,
true, false, false, false, true, false, true,
false,false,false,true,false,true,false};
private void button1_Click(object sender, EventArgs e) {
int Value = Convert.ToInt32(textBox1.Text);
if ((Value >= 0) && (Value < Primes.Length)) {
bool IsPrime = Primes[Value];
textBox2.Text = IsPrime.ToString();
}
}
Maybe you want to see if a character in a string is hexadecimal. You could use an ungly and somewhat large switch statement.
Or you could use either regular expressions to test the char or use the IndexOf function to search for the char in a string of known hexadecimal letters:
private void textBox2_TextChanged(object sender, EventArgs e) {
try {
textBox1.Text = ("0123456789ABCDEFGabcdefg".IndexOf(textBox2.Text[0]) >= 0).ToString();
} catch {
}
}
Let us say you want to do one of 3 different actions depending on a value that will be the range of 1 to 24. I would suggest using a set of IF statements. And if that became too complex (Or the numbers were larger such as 5 different actions depending on a value in the range of 1 to 90) then use an enum to define the actions and create an array map of the enums. The value would then be used to index into the array map and get the enum of the action you want. Then use either a small set of IF statements or a very simple switch statement to process the resulting enum value.
Also, the nice thing about an array map that converts a range of values into actions is that it can be easily changed by code. With hard wired code you can't easily change behaviour at runtime but with an array map it is easy.
A more beautiful way to handle that
if ([4, 5, 6, 7].indexOf(value) > -1)
//Do something
You can do that for multiple values with the same result
Just to add to the conversation, using .NET 4.6.2 I was also able to do the following.
I tested the code and it did work for me.
You can also do multiple "OR" statements, like below:
switch (value)
{
case string a when a.Contains("text1"):
// Do Something
break;
case string b when b.Contains("text3") || b.Contains("text4") || b.Contains("text5"):
// Do Something else
break;
default:
// Or do this by default
break;
}
You can also check if it matches a value in an array:
string[] statuses = { "text3", "text4", "text5"};
switch (value)
{
case string a when a.Contains("text1"):
// Do Something
break;
case string b when statuses.Contains(value):
// Do Something else
break;
default:
// Or do this by default
break;
}
We can also use this approach to achieve Multiple cases in switch statement... You can use as many conditions as you want using this approach..
int i = 209;
int a = 0;
switch (a = (i>=1 && i<=100) ? 1 : a){
case 1:
System.out.println ("The Number is Between 1 to 100 ==> " + i);
break;
default:
switch (a = (i>100 && i<=200) ? 2 : a) {
case 2:
System.out.println("This Number is Between 101 to 200 ==> " + i);
break;
default:
switch (a = (i>200 && i<=300) ? 3 : a) {
case 3:
System.out.println("This Number is Between 201 to 300 ==> " + i);
break;
default:
// You can make as many conditions as you want;
break;
}
}
}
Using new version of C# I have done in this way
public string GetValue(string name)
{
return name switch
{
var x when name is "test1" || name is "test2" => "finch",
"test2" => somevalue,
_ => name
};
}
For this, you would use a goto statement. Such as:
switch(value){
case 1:
goto case 3;
case 2:
goto case 3;
case 3:
DoCase123();
//This would work too, but I'm not sure if it's slower
case 4:
goto case 5;
case 5:
goto case 6;
case 6:
goto case 7;
case 7:
DoCase4567();
}