i have problem in String.Replace() method

Then Replace is not for you - either use IndexOf and Substring to replace the data manually, or use a Regex to do a more sophisticated pattern matching and replacement.

From your brief description it is difficult to tell, but if you want to change:

a.set(a_Value, comment= a_Comment', report= 0, format= '%s')

To

Replaced.set(a_Value, comment= a_Comment', report= 0, format= '%s')

Then this might do it:

Regex reg = new Regex("\\w+(?=\\.set)");
string result = reg.Replace(InputText,"Replaced");

But it's difficult to tell from a single example of the input with no output samples.

Hi

var myString = "a.set a.set(a_Value, comment= a_Comment', report= 0, format= '%s')";

//If you want to replace only 'a.' to something else like 'b.':
var replaced = myString.Replace("a.", "b.");


//If you want to replace all 'a's except 'a_':

var sb = new StringBuilder();

for(var i =0;i<mystring.length;i++)>
{
    var c = myString[i];

    if (c=='a' && i < myString.Length - 1 && myString[i + 1]!= '_')
    {
        c = 'b';
    }
    sb.Append(c);
}

replaced = sb.ToString();