Hi,
I am creating an application through which I can read a text file saved on my disk and find the block of strings through specified array of spans (start and end positions of strings to find) then after I need to replace these blocks of string with other block of string and create a new text file so that at the end I can have 2 text files old one and the modified new one.

I am explaining this with an example:--
lets say I have a text file old.txt which contains following data in it:
Find the formula to calculate area of a circle.
Find the formula to calculate area of a square.
Find the formula to calculate area of a rectangle.
Find the formula to calculate area of a tringle.
and so on..

now I need to modify this text file with following new data and create the new.txt file for which I will pass the span values of "formula" like start value=9 and end value=16 for 1st sentence and so on..:
Find the <Math> formula <Equation> to calculate area of a circle.
Find the <Math> formula <Equation> to calculate area of a square.
Find the <Math> formula <Equation> to calculate area of a rectangle.
Find the <Math> formula <Equation> to calculate area of a tringle.


Can anyone help me to acheive this.

Thanks in advance.

If you read the text from the file into an array of strings (e.g. File.ReadAllLines() method), then you just need to do two Insert commands. Use a StringBuilder for your output text.

string[] lines = File.ReadAllLines("C:\\test.txt");

int pos1 = 9;
string insert1 = "<Math>";
int pos2 = 16 + insert1.Length;
string insert2 = "<Equation>";

StringBuilder output = new StringBuilder();

foreach(string s in lines)
{
    string t = s.Insert(pos1, insert1);
    output.Append(t.Insert(pos2, insert2));
}

// now write out output.ToString()

/- Sam Judson : Wrox Technical Editor -/

Thanks for your guidance..
but this approach will not be good if the size of text file is big.
And according to your aproach start and end span is always 9 and 16 respectively but this is not the case, for second sentence span values are 57 and 64 respectively and so on..

Thanks..

My method splits the text file into a number of lines - you are only counting from the start of the line, not from the start of the text file. Therefore assuming your example is a valid example it would be the 9th and 16th characters on each and every line.

/- Sam Judson : Wrox Technical Editor -/