[UWP] How to check if string equals to "_n_"

Question

Hello,

How to check if string equals to expresion showed in post title, where n is number (1,2,3,4,5,6, etc).

Note, I dont want chceck if string contains such expresion, I need to konow if the string exactly equals to expresion.

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

According to your needs, you want the string to be tested to fully conform to the form _n_, with no extra strings before and after. This situation can be solved using regular expressions:

var regex = new Regex(@"^_\d+_$");
if(regex.IsMatch(inputString))
{
// do something
}

---

Update

May I know the language you are using? I implemented it using C#.

Regular expressions have a large overhead on system resources. If there are no special requirements, you can consider this method:

public bool IsMatchNeeds(string inputString)
{
    if (inputString.Length < 3)
        return false;
    bool isFirst = inputString.First().Equals("_");
    bool isLast = inputString.Last().Equals("_");
    if (isFirst && isLast)
    {
        string numberString = inputString.Replace("_", "");
        bool isNumber = int.TryParse(numberString, out int num);
        return isNumber;
    }
    return false;
}

Usage

if(IsMatchNeeds(inputString))
{
    // do something...
}

There are several ways to check if a string is a number. In addition to the regular expressions mentioned earlier, there are the following methods:

1. Enumerable.All

bool isNumber = numberString.All(p => char.IsDigit(p));

2. Enumerable.Any

bool isNumber = !numberString.Any(p => p < '0' || p > '9');

3. int.TryParse

bool isNumber = int.TryParse(numberString, out int number);

4. for-each loop

bool isNumber = true;
foreach (var p in numberString)
{
    if (p < '0' || p > '9')
    {
        isNumber = false;
        break;
    }   
}

Thanks.