{3} in regex mean exactly 3 times but

Question

hello. I use this pattern in my c# application (\d+){3} and I get matches like 245 , 5678 , 123456 , 678 . . . when I expect to get exactly {3} 3 numbers with digits size of 1 or greater. please can someone explain what is my wrong. thank you very much

Answer 1

Hi @Haviv Elbsz , Welcome to Microsoft Q&A,

I think you should use it in conjunction with code judgment.

Don't when the number in the obtained group is greater than 3.

make judgments

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Windows.Forms;

namespace xxx
{
     public partial class Form1 : Form
     {
         public Form1()
         {
             InitializeComponent();
         }

         private void Form1_Load(object sender, EventArgs e)
         {
             textBox1.Text = "6";
             textBox2.Text = "34sad 464dff";
             textBox3.Text = "34sad 464dff asdas 45647ff";
             textBox4.Text = "34sad 464dff 546asdas 45647ff";
         }

         //Use the regular \d+( \d+){0,2} to determine that the content in the textbox is returned as a list. If the elements of the list are more than 3 or equal to 0, false is returned.
         static List<int> ExtractNumbers(string input)
         {
             List<int> result = new List<int>();

             //Define regular expression
             Regex regex = new Regex(@"\d+( \d+)?( \d+)?");

             // Match string
             MatchCollection matches = regex.Matches(input);

             //Extract matching numbers
             foreach (Match match in matches)
             {
                 foreach (Capture capture in match.Captures)
                 {
                     int number;
                     if (int.TryParse(capture.Value, out number))
                     {
                         result.Add(number);
                     }
                 }
             }

             return result;
         }

         static bool isValid(List<int> numbers)
         {
             if (numbers.Count == 0 || numbers.Count > 3)
             {
                 return false;
             }
             else
             {
                 return true;
             }
         }
         private void button1_Click(object sender, EventArgs e)
         {
             foreach (Control c in this.Controls)
             {
                 if (c is TextBox)
                 {
                     List<int> numbers = ExtractNumbers(c.Text);

                     if (isValid(numbers))
                     {
                         c.Text += "Valid";
                     }
                     else
                     {
                         c.Text += "inValid";
                     }
                 }
             }
         }
     }
}

Best Regards,

Jiale

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Answer 2

I think that you should use (\d{3})+.

A number like 5678 is matched by (\d+){3} because \d+ can be repeated three times: \d\d, \d, \d.

Or use ^(\d{3})+$ depending on context.