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Unexpected results for checking if a character is a symbol

I am creating a string extension to check if a string is all symbols or not however it is not working as I would expect it to, so far I have the following:

// Class for: String extensions
public static class StringExtension

// Method for: Determining if a string contains only symbols
public static bool ContainsOnlySymbols(this String inputString)

// Identifiers used are:
bool containsMore = false;

// Go through the characters of the input string checking for symbols
foreach (char character in inputString.ToCharArray())
Char.IsPunctuation(character) also
// Credit: @asantaballa
containsMore = Char.IsSymbol(character) ? false : true;
if (containsMore)

return containsMore;



// Return the results
return containsMore; // Edited after answer: <-- mistake here




Now if I use this extension on the following two strings I get the opposite of what I expect to see:

string testString = "!=";


I expect this to be all symbols, but

I expect: testString.ContainsOnlySymbols() => true
I get: testString.ContainsOnlySymbols() => false


Now if I use the next test string:

string testString = "Starts with";


I expect this to have no symbols

I expect: testString.ContainsOnlySymbols() => false
I get: testString.ContainsOnlySymbols() => true


4 Answers
4

A couple problems:

In your loop, you are really only getting the option related to the last character. And or clause should take care of it.

containsMore = containsMore || !(Char.IsSymbol(character) || Char.IsPunctuation(character));


Then, you need a not at the end. If it doesn't contain more, then its only symbols

return ! containsMore;


You might want a special case for how to handle empty strings too. Not sure how you want to handle that. That will be your choice if an empty string should return true or false.

You can accomplish this with a one-liner. See these examples.

string x = "@#=";
string z = "1234";
string w = "1234@";

bool b = Array.TrueForAll(x.ToCharArray(), y => (Char.IsSymbol(y) || Char.IsPunctuation(y))); // true
bool c = Array.TrueForAll(z.ToCharArray(), y => (Char.IsSymbol(y) || Char.IsPunctuation(y))); // false
bool e = Array.TrueForAll(w.ToCharArray(), y => (Char.IsSymbol(y) || Char.IsPunctuation(y))); // false


Checking all chars if all isSymbol or Punctuation. we return true here.

public static bool ContainsOnlySymbols(this String inputString)

return inputString.ToCharArray().All(x => Char.IsSymbol(x)


Test:

string testString = "Starts with"; // => false
string testString = "!="; // => true
string testString = "@@"; // => true
string testString = "!Starts with"; // => false


I believe the IsSymbol method checks for a very specific set of character. You may want to do:

containsMore = (Char.IsSymbol(character) || Char.IsPunctuation(character)) ? false : true;


Wrote a quick program to show results for character and does show symptom. Might even be that all you need for your app is IsPunctuation.

33/!: IsSymbol=False, IsPunctuation=True


Program

using System;

namespace csharptestchis

class Program

static void Main(string args)

for (int i = 0; i <= 255; i++)

char ch = (char)i;
bool isSymbol = Char.IsSymbol(ch);
bool isPunctuation = Char.IsPunctuation(ch);
Console.WriteLine($"i/ch: IsSymbol=isSymbol, IsPunctuation=isPunctuation ");






Firstly, the idea is simple: you loop your string, if you meet a character non-symbol, return false. Until the end of string and you don't meet a character non-symbol. Voilà, return true.

string

false

string

true

public static bool ContainsOnlySymbols(string inputString)

// Identifiers used are:
bool containsMore = false;

// Go through the characters of the input string checking for symbols
foreach (char character in inputString)

containsMore = Char.IsSymbol(character) ? false : true;
if(!containsMore)
return false;


// Return the results
return true;



Secondly, there is a problem with your code, IsSymbol returns true only if your character is in these groups

IsSymbol

MathSymbol, CurrencySymbol, ModifierSymbol, and OtherSymbol.

And fortunately, ! don't be in these groups. That means "!=" returns false.

!

false

So you must include others conditions like:

public static bool ContainsOnlySymbols(string inputString)
Char.IsPunctuation(c));



Or you have to write your own method to determine what symbol is acceptable and what is not.

Or if a string doesn't contain digit and letter, it can be considered symbol. You can do

public static bool ContainsOnlySymbols(string inputString)

// Go through the characters of the input string checking for symbols
return !inputString.Any(c => Char.IsLetterOrDigit(c));



ToCharArray

string

IEnumerable<char>

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