在richTextBox1中随机出了好多加减乘除题想要判断题对错怎么办

在richTextBox1中随机出了好多加减乘除题想要判断题对错怎么办

 using System.Text.RegularExpressions;

bool foo(string s)
{
    var m = Regex.Match(s, @"(\d+)([\+\-\*\/])(\d+\)=(\d+)");
        int n1 = int.Parse(m.Groups[1].Value);
        int n2 = int.Parse(m.Groups[3].Value);
        int n3 = int.Parse(m.Groups[4].Value);
        char op = m.Groups[2].Value[0];
        int r = 0;
        switch (op)
        {
            case '+': r = n1 + n2; break;
                case '-' : r = n1 - n2; break;
                case '*' : r = n1 * n2; break;
                case '/' : r = n1 / n2; break;
        }
        return r == n3;
}