Question

I am having string variable as follow

 string pctSign = "\0\0\0";

I want to replace first two characters with “%”

i.e. Final o/p:- pctSign="%\0\0";

How to do this with String.Replace?

Answer 1

// Option 1
var result = "%" + pctSign.Remove(0, 2);

// Option 2
var result = "%" + pctSign.Substring(2);

// Option 3
var regex = new Regex("^\\0");
var result = regex.Replace(pctSign, "%");

If you absolutely want to user String.Replace() then you can write your own extension method:

public static class StringExtension
{
    public static String Replace(this string self, 
                                      string oldString, string newString, 
                                      bool firstOccurrenceOnly = false)
    {
        if ( !firstOccurrenceOnly )
            return self.Replace(oldString, newString);

        int pos = self.IndexOf(oldString);
        if ( pos < 0 )
            return self;

        return self.Substring(0, pos) + newString 
               + self.Substring(pos + oldString.Length);
    }
}

// Usage:
var result = pctSign.Replace("/0", "%", true);