Validate mathematical expressions using regular expression?

Question

I want to validate mathematical expressions using regular expression. The mathematical expression can be this

1. It can be blank means nothing is entered

Answer 1

If you want negative or positive expression you can write it like this>
^\-?[0-9](([-+/*][0-9]+)?([.,][0-9]+)?)*?$

And a second one
^[(]?[-]?([0-9]+)[)]??([(]?([-+/*]([0-9]))?([.,][0-9]+)?[)]?)*$

With parenthesis in expression but doesn't count the number you will need method that validate it or regex. // the method

 public static bool IsPairParenthesis(string matrixExpression)
    {
        int numberOfParenthesis = 0;
        foreach (char character in matrixExpression)
        {
            if (character == '(')
            {
                numberOfParenthesis++;
            }
            if (character == ')')
            {
                numberOfParenthesis--;
            }
        }

        if (numberOfParenthesis == 0)
        { return true; }
        return false;
    }

Answer 2

Something like this should work:

^([-+/*]\d+(\.\d+)?)*

Regexr Demo

• ^ - beginning of the string
• [-+/*] - one of these operators
• \d+ - one or more numbers
• (\.\d+)? - an optional dot followed by one or more numbers
• ()* - the whole expression repeated zero or more times

Answer 3

This is java regex, but this is only if not have any braces

[+\-]?(([0-9]+\.[0-9]+)|([0-9]+\.?)|(\.?[0-9]+))([+\-/*](([0-9]+\.[0-9]+)|([0-9]+\.?)|(\.?[0-9]+)))*

Also this with braces in java code
In this case I raplace (..) to number (..), should matches without brace pattern

    //  without brace pattern
    static Pattern numberPattern = Pattern.compile("[+\\-]?(([0-9]+\\.[0-9]+)|([0-9]+\\.?)|(\\.?[0-9]+))([+\\-/*](([0-9]+\\.[0-9]+)|([0-9]+\\.?)|(\\.?[0-9]+)))*");
    static Pattern bracePattern = Pattern.compile("\\([^()]+\\)");

    public static boolean matchesForMath(String txt) {

        if (txt == null || txt.isEmpty()) return false;
        txt = txt.replaceAll("\\s+", "");
        if (!txt.contains("(") && !txt.contains(")")) return numberPattern.matcher(txt).matches();
        if (txt.contains("(") ^ txt.contains(")")) return false;
        if (txt.contains("()")) return false;

        Queue<String> toBeRematch = new ArrayDeque<>();
        toBeRematch.add(txt);
        while (toBeRematch.size() > 0) {
            String line = toBeRematch.poll();
            Matcher m = bracePattern.matcher(line);
            if (m.find()) {
                String newline = line.substring(0, m.start()) + "1" + line.substring(m.end());
                String withoutBraces = line.substring(m.start() + 1, m.end() - 1);
                toBeRematch.add(newline);
                if (!numberPattern.matcher(withoutBraces).matches()) return false;
            }

        }
        return true;
    }