Tips for code-golfing in C#

Question

What general tips do you have for golfing in C#? I'm looking for ideas that can be applied to code golf problems in general that are at least somewhat specific to C# (e.g. "remove comments" is not an answer). Please post one tip per answer.

-- borrowed from marcog's idea ;)

Answer 1

Instead of using .ToString() use +"" for numerics and other types that can be natively cast to a string safely.

.ToString() <-- 11 chars
+""         <--  3 chars

Answer 2

I once deliberately placed my program in namespace System so I can shorten access to a specific class. Compare

using System;using M=System.Math;

to

namespace System{using M=Math;

Answer 3

If using LINQ you can pass a method directly to Select instead of making a lambda.

So, instead of

foo.Select(x=>int.Parse(x))

you can use

foo.Select(int.Parse)

directly.

(Discovered recently when improving on one of Timwi's C# answers.)

Answer 4

Use var for declaring and initializing (single) variables to save characters on the type:

string x="abc";

becomes

var x="abc";

Isn't particulaly necessary for int, of course.

Answer 5

Remember that the smallest compilable program in C# is 29 characters:

class P
{
    static void Main()
    {   
    }
}

So start by removing that from your length and judge your answer on how much over that it takes. C# cannot compete with other languages when it comes to printing or reading input, which is the heart of most [code-golf] problems, so don't worry about that. As a C# golfer, you're really competing against the language.

A few other things to keep in mind:

• Reduce all loops and if statements to a single line if possible in order to remove the brackets.
• If given the option between stdin and command line, always use command line!

Answer 6

Instead of

bool a = true;
bool b = false;

do

var a=0<1;
var b=1<0;

If you need multiple variables, use this (suggested by @VisualMelon)

bool a=0<1,b=!a;

Answer 7

When reading each character of a command line argument, rather than looping up to the string's length:

static void Main(string[]a){
    for(int i=0;i<a[0].Length;)Console.Write(a[0][i++]);
}

You can save a character by using a try/catch block to find the end:

static void Main(string[]a){
    try{for(int i=0;;)Console.Write(a[0][i++]);}catch{}
}

This applies to any array within an array such as:

• string[]
• int[][]
• IList<IList<T>>

Answer 8

If you need to use Console.ReadLine() multiple times in your code (min 3 times), you could do:

Func<string>r=Console.ReadLine;

and then just use

r()

instead

Answer 9

Favor the ternary operator over if..else blocks where appropriate.

For example:

if(i<1)
    j=1;
else
    j=0;

is more efficiently:

j=i<1?1:0;

Answer 10

Effective use of using

You can replace float (which is an alias for System.Single) with z using z=System.Single;

Then replace z=System.Single; with z=Single; by placing the program in the namespace System. (As with Joey's answer)

This can be applied for other value types (use what they are an alias for), structs and classes

Answer 11

LINQ

Instead of using:

Enumerable.Range(0,y).Select(i=>f(i))

to get an Enumerable with the result of function f for every int in [0,y] you can use

new int[y].Select((_,i)=>f(i))

if you need string or anything that implements Enumerable in your program you can use them too

var s="I need this anyway";
s.Select((_,i)=>f(i))

Answer 12

In C#, we are not allowed to do if(n%2) to check if n is a even number. If we do, we get a cannot implicity convert int to bool. A naive handling would be to do:

if(n%2==0)

A better way is to use:

if(n%2<1)

I used this to gain one byte here.

note that this only works for positive numbers, as -1%2==-1, it is considered even with this method.

Answer 13

Use lambdas to define a function in C# 6

In C# 6, you can use a lambda to define a function:

int s(int a,int b)=>a+b;

This is shorter than defining a function like this:

int s(int a,int b){return a+b;}

Answer 14

Looping:

Variable declarations:

int max;
for(int i=1;i<max;i++){
}

become:

int max,i=1;
for(;i<max;i++){
}

And if you have a need to or work with the i variable only once, you could start at -1 (or 0 depending on the loop circumstance) and increment inline:

int max,i=1;
for(;i<max;i++){
  Console.WriteLine(i);
}

to

int max,i=1;
for(;i<max;){
  Console.WriteLine(++i);
}

And that reduces by one character, and slightly obfuscates the code as well. Only do that to the FIRST i reference, like thus: (granted one character optimizations aren't much, but they can help)

int max,i=1;
for(;i<max;i++){
  Console.WriteLine(i + " " + i);
}

to

int max,i=1;
for(;i<max;){
  Console.WriteLine(++i + " " + i);
}

---

when the loop does not have to increment i (reverse order loop):

for(int i=MAX;--i>0;){
      Console.WriteLine(i);
}

Answer 15

If you need to use a generic Dictionary<TKey, TValue> at least two times in your code, you could declare a dictionary class, like in this example:

class D:Dictionary<int,string>{}

and then just use

D d=new D{{1,"something"},{2,"something else"}};

instead of repeating Dictionary<int,string> for every instantiation.

I have used this technique in this answer

Answer 16

For one-line lambda expressions, you can skip the brackets and semicolon. For one-parameter expressions, you can skip the parentheses.

Instead of

SomeCall((x)=>{DoSomething();});

Use

SomeCall(x=>DoSomething);

Answer 17

You can use float and double literals to save a few bytes.

var x=2.0;
var y=2d;         // saves 1 byte

When you need some int arithmetic to return a float or double you can use the literals to force the conversion.

((float)a+b)/2;  // this is no good
(a+b)/2.0;       // better
(a+b)/2f;        // best      

If you ever run into a situation where you have to to cast you can save a few bytes by using multiplication instead.

((double)x-y)/(x*y);
(x*1d-y)/(x*y);      // saves 5 bytes

Answer 18

Avoid single-statement foreach loops

If the loop's statement returns a non-int (including void!) "value", it can be replaced with LINQ:

foreach(var x in a)Console.WriteLine(F(x));
a.Any(x=>Console.WriteLine(F(x))is int);

If the value happens to be an int, you can use a condition that will always be true or always be false (for example, >0 or <n), a different type and/or All instead of Any.

Answer 19

Remember where private or public are inherent, such as the following:

class Default{static void Main()

as compared to

public class Default { public static void Main()

Answer 20

There are circumstances when an output parameter can save characters. Here's a slightly contrived example, a 10 pin bowling score algorithm.

With a return statement:

........10........20........30........40........50........60........70........80........90.......100.......110.......120.......130.......140.......150..
public double c(int[]b){int n,v,i=0,X=10;double t=0;while(i<19){n=b[i]+b[i+1];v=b[i+2];t+=(n<X)?n:X+v;if(b[i]>9)t+=b[i+(i>16|v!=X?3:4)];i+=2;}return t;}

And with an output parameter:

........10........20........30........40........50........60........70........80........90.......100.......110.......120.......130.......140.......
public void d(int[]b,out double t){int n,v,i=0,X=10;t=0;while(i<19){n=b[i]+b[i+1];v=b[i+2];t+=(n<X)?n:X+v;if(b[i]>9)t+=b[i+(i>16|v!=X?3:4)];i+=2;}}

The output parameter here saves a total of 5 characters.

Answer 21

Use dynamic to group declarations

dynamic is a forgotten feature that literally performs dynamic typing in C#! It has limitations (doesn't support extension methods, is bad at inferring that you want to use it, ...), but can often save bytes by merging declarations of incompatible types. Compare the following:

var a=[something of type IEnumerable<int>];var b=[something of type string];int i=x+~y^z
dynamic a=[something of type IEnumerable<int>],b=[something of type string],i=x+~y^z

That's 4 bytes of savings!

Answer 22

String Interpolation

A really simple space-saving improvement is interpolation. Instead of:

string.Format("The value is ({0})", (method >> 4) + 8)

just use $ to inline expressions:

$"The value is ({(method >> 4) + 8})"

This, together with the new expression bodies in C#6.0 should make any simple string-calculation challenge pretty golfable in C#.

Answer 23

Use the weird kind of the is operator

a is var b always defines the variable b equal to a and returns true. It is unclear how have the humans who design C# come up with this (inline variable declarations that return true for some reason seem to be beyond Javascript to me), but it works. It can sometimes be used to shorten code (this is an oversimplified example; savings can often be smaller or zero):

a=>{var b=f(a);return g(b,b);}
a=>g(f(a)is var b?b:b,b)

Answer 24

If you need to include multiple usings that all fall off of the same hierarchy it is often shorter to use the longest one as the namespace:

using System;
using System.Linq;
//Some code

vs:

namespace System.Linq
{
    //Some code
}

Answer 25

The Compute instance method of System.Data.DataTable, allows to evaluate a simple string expression, e.g. :

C# (Visual C# Compiler), 166 bytes

namespace System.Data
{
    class P
    {
        static void Main()
        {
            Console.Write(new DataTable().Compute("30*2+50*5/4",""));
        }
    }
}

Try it online!

Not very "golfy" per se, but sometimes might be useful.

Answer 26

Swapping two variables

Normally, to swap two variables, you have to declare a temporary variable to store the value. It would look like something along the lines of this:

var c=a;a=b;b=c;

That's 16 bytes! There are some other methods of swapping that are better.

//Using tuples
(a,b)=(b,a);
//Bitwise xoring 
a=a^b^(b=a);
//Addition and subtraction
a=a+b-(b=a);
//Multiplication and division
a=a*b/(b=a);

The last three only work for numeric values, and as ASCII-only pointed out, the last two might result in an ArithmeticOverflow exception. All of the above are 12 bytes, a 4 byte saving compared to the first example.

Answer 27

Use C# lambda. Since PPCG allows lambda for input/output we should use them.

A classic C# methods looks like this:

bool Has(string s, char c)
{
    return s.Contains(c);
}

As a lambda, we will write

Func<string, char, bool> Has = (s, c) => s.Contains(c);

Anonymous lambda are allowed too:

(s, c) => s.Contains(c)

Remove all the noise and focus!

Update:

We can improve one step more with currying as @TheLethalCoder comment:

s => c => s.Contains(c);

Example of curring by @Felix Palmen: How compute WPA key?

It will be helpful when you have exactly 2 parameters, then a empty unused variable _ will be better. See meta post about this. I use this trick here. You will have to change a bit the function. Example: Try it online!

Answer 28

Use .NET 6 Top Level Statements, File-Scoped Namespaces, and target-typed new()

Upgrade to .net 6 and you can use single file programs with no boilerplate. You can also use file-scoped namespaces like so:

namespace whatever;

Also, when you instantiate an object, if it's type can be inferred by the compiler, you can use a target-typed new() constructor. e.g.,

class C {}
C c=new();

See (https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/top-level-statements)

See Also (https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-10.0/file-scoped-namespaces)

Answer 29

Make classnames only one letter. Enhancing on Tips for code-golfing in C# we go from

class Default{static void Main()

to

class D{static void Main()

which knocks out another 6 chars in this case.

Answer 30

Group statements via tuples

Let's assume the simplest case: you have two statements that return a value and would like to group them into one that returns the second value (perhaps the first one has useful side effects):

(s1,o:s2).o

This can be used along with inline variable declarations via is:

(s1 is var x,o:f(x,g(x))).o

It also works with the void -> value transformation via is int (although it doesn't always help):

(Print(x)is int,o:f(x)).o