Check string contains mathematical symbols inside it in C#

There's a standard function for this, find_first_of.

http://www.cplusplus.com/reference/string/string/find_first_of/

"Find character in string
Searches the string for the first character that matches any of the characters specified in its arguments."

In .Net is a different way than in C++: string.IndexOf. https://docs.microsoft.com/en-us/dotnet/api/system.string.indexof?view=netframework-4.8

Go with Rikin's answer.  Index of will give you. Number for the position (0 based) of a single character.  IndexOfAny will take a character array and will return the first position it finds.  If nothing is found by either of these methods the return value is -1.  Since the string is treated as an array all positions will be 0 based if that is at all useful for you to further develop this bit of code.

If the method returns -1 you can return False else True.

the original post requires to return True if  no math operator could be found (see also sample output it_saige has posted).

beside of that i support Rikin's solution using String.IndexOfAny which exactly does what was asked for.

public static bool HasNoMathOps(String str)
{
      char [] mathops = { '+', '-', '*', '/', '^' };
      return (str.IndexOfAny(mathops) < 0); 
}

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however, returning a bool (only) gives away the additional information IndexOfAny could provide. for example if you want to parse an expression which might contain operators or even if you want to program a calculator.

enum MathOp { noop = -1, plus, minus, times, divided, power };
public static MathOp FindNextMathOp(String str, ref int pos)
{
      char [] mathops = { '+', '-', '*', '/', '^' };
      // start at position given by pos
      pos = str.IndexOfAny(mathops, pos);
       if (pos >= 0) 
       {
              return (MathOp)Array.IndexOf(mathops, str[pos]);
       }
       return noop; 
}

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you could use the function like

   string s = "1 + (5 - 7) * 2 + (2^x))";  
   int pos = 0;
   MathOp op = noop;
   while ((op = FindNextMathOp(s, pos)) != noop)
   {
          Console.WriteLine("Operator {0} found at position {1}\n", op.ToString(), pos):
          pos++;
   }

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(code not tested).

Sara

Hi Hakan,

i would suggest using the regular expression because it gives you flexibility and not limit you to fixed set of characters if you want to go this approach. Please see the below code and change it as per your requirement. Also if you want to know more about regular expression in C# and how you can leverage the power of RegEx please go through this article: System.Text.RegularExpressions Namespace

using System;
using System.Text.RegularExpressions;


public class Program
{
  public static void Main()
  {
    string text = "Find symbol +$-/# in this string";
    string pat = @"\W";

    // Instantiate the regular expression object.
    Regex r = new Regex(pat, RegexOptions.IgnoreCase);
    
    // Match the regular expression pattern against a text string or symbol.
    Match m = r.Match(text);

    if(m.Success)
    {
      Console.WriteLine("Match found for symbol!!!");
    }
  }  
}

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Output:

regular expressions have a few disadvantages: the syntax is rather complex and you need much time and patience before you safely could use them. then, beside of trivial cases there is no proof that an expression that is valid for a set of sample strings would give a valid match for all strings. any change of the expressions requires to repeat all tests made before to make sure that the change wouldn't affect the match results so far. finally, for a rather simple problem to check whether an expression contaiins some math characters, the regex functions are pure overkill regarding both the efforts to define the expression and the costs of execution.

the function String.IndexOfAny suggested by Rikin is the right way to go.

Sara