Develop Reference

Why is this function crashing my program?

I'm new in programming and this is my first project and I'm using C#. Basically I tryed to do a function that insert one more single quote in string that already have a single quote, but this is crashing my program and I don't know why.
The function:
private string CheckSingleQuote(string txt)
{
for (int i = 0; i < txt.Length; i++)
if (txt[i] == '\'')
txt = txt.Insert(i, "'");
return txt;
}
When I click in a specific button, this function is called ten times to set the value of the strings.

You can do String.Replace("'", "''") or if you want to use the for:
private string CheckSingleQuote(string txt)
{
for (int i = 0; i < txt.Length; i++)
if (txt[i] == '\'')
txt = txt.Insert(i++, "'");
return txt;
}
As mjwills said in the comment the i++ is to skip the ' character that you just inserted.

How to include two text boxes texts?

I want to include two text box texts to one text box like this
both of them are multiline.
But I want special form of include, in other words I want to include them like this
textbox 1 texts: '' help''' '' other''
textbox 2 texts:' 1' '2' '' 3''
results: help1 _ help2 _ help3
other1_other2_other3

Multiline textboxes return a string array with the lines in the Lines property. You could do something like this
string[] words = textBox1.Lines;
string[] numbers = textBox2.Lines;
var resultLines = new string[words.Length];
var sb = new StringBuilder();
for (int i = 0; i < words.Length; i++) {
sb.Length = 0; // Reset StringBuilder for the next line.
for (int j = 0; j < numbers.Length; j++) {
sb.Append(words[i]).Append("-").Append(numbers[j]).Append("_");
}
if (sb.Length > 0) {
sb.Length--; // remove the last "_"
}
resultLines[i] = sb.ToString();
}
resultsTextBox.Lines = resultLines;
First we get the words and numbers arrays. Then we create a new array for the result. Since we want a result line for each word, we make it words.Length in size.
Then we loop through the words. We use a StringBuilder to build our new lines. This is more efficient as concatenation strings with +, as it minimizes copy operations and memory allocations.
In a nested loop we put the words and numbers together.

An elegant way to solve your issue is to make use of the String.Join method in C#. I'm adding this answer because I'm a big fan of the method and think it must be part of some answer to this question because it has to do with combining strings.
Here's the code that I'd use to solve the challenge:
string[] firstInput = textBox1.Lines;
string[] secondInput = textBox2.Lines;
var combinedInputs = new string[firstInput.Length];
var combinedLine = new string[secondInput.Length];
for(int i = 0; i < firstInput.Length; i++)
{
for(int j = 0; j < secondInput.Length; j++)
{
combinedLine[j] = firstInput[i] + secondInput[j];
}
//Combine all values of combinedLine with a '-' in between and add this to combinedInputs.
combinedInputs[i] = String.Join("-", combinedLine);
}
outputTextBox.Lines = combinedInputs; //the resulting output
I hope this answer helped aswell. And I'd like to give credits to Olivier for explaining the textbox part. Another thing that I'd like to add is that this answer isn't meant to be the most efficient, but is meant to be easy to read and understand.

WPF paste unicode text with newlines into multiple textboxes

I generate textboxes like so:
for (byte i = 0; i < 4; ++i)
for (byte j = 0; j < 4; ++j)
Letterbox[i, j] = new TextBox();
Letterbox[i, j].Style = style; //MaxLength=1 among other things
...
and I'd wish that pasting string like this:
T
Ę
Ś
T
would result in first 4 textboxes containing 'T', 'Ę', 'Ś' and 'T' consecutively.
How can I achieve this?
Clarification (edit):
I want to be able to paste any string in this format (letter, enter, letter, enter...) when the application is running, not hardcode it
Here's an image explaining what I want.

You can use AddPasteHandler
like so:
DataObject.AddPastingHandler(tb, OnPaste);
OnPaste method implementation:
private void OnPaste(object sender, DataObjectPastingEventArgs e)
{
var isText = e.SourceDataObject.GetDataPresent(DataFormats.UnicodeText, true);
if (!isText) return;
var text = e.SourceDataObject.GetData(DataFormats.UnicodeText) as string;
HandlePaste(text);
e.Handled = true;
}
private void HandlePaste(string text)
{
var letters = text.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
if (letters.Length == 4)
{
for (var i = 0; i < 4; i++)
{
Letterbox[0, i].Text = letters[i];
}
}
}
tb is some other TextBox on my window, you can use whatever suits your requirements.
In HandlePaste pasted string is split by newlines and when it fits into 4 textboxes Text of each of them is set to appropriate letter. You could add some more validation here like checking if each of strings is exactly one char in length.

Moving in text file with C#

I have a problem with C#.
I am writing code to search a text file until it finds a certain word, then the code should move three lines and read the fourth, then continue the search to find the certain word again.
Now I don't know how to navigate through the file (forward and backward) to the line I want.
Can anybody help?

You can do something like this:
var text = File.ReadAllLines("path"); //read all lines into an array
var foundFirstTime = false;
for (int i = 0; i < text.Length; i++)
{
//Find the word the first time
if(!foundFirstTime && text[i].Contains("word"))
{
//Skip 3 lines - and continue
i = Math.Min(i+3, text.Length-1);
foundFirstTime = true;
}
if(foundFirstTime && text[i].Contains("word"))
{
//Do whatever!
}
}

// read file
List<string> query = (from lines in File.ReadLines(this.Location.FullName, System.Text.Encoding.UTF8)
select lines).ToList<string>();
for (int i = 0; i < query.Count; i++)
{
if (query[i].Contains("TextYouWant"))
{
i = i + 3;
}
}

Your requirements state that you are searching for a specific word. If that is true and you are not instead looking for a specific string, then the checked answer on this is wrong. Instead you should use:
string[] lines = System.IO.File.ReadAllLines("File.txt");
int skip = 3;
string word = "foo";
string pattern = string.Format("\\b{0}\\b", word);
for (int i = 0; i < lines.Count(); i++)
{
var match = System.Text.RegularExpressions.Regex.IsMatch(lines[i], pattern);
System.Diagnostics.Debug.Print(string.Format("Line {0}: {1}", Array.IndexOf(lines, lines[i], i) + 1, match));
if (match) i += skip;
}
If you use the string.contains method and the word you are searching for is "man", while your text somewhere contains "mantle" and "manual", the string.contains method will return as true.

Special characters in string.Replace

I want to replace special characters in string.
For example this is input text
http\u00253A\u00252F\u00252Fvideo.l3.fbcdn.net\u00252Fcfs-l3-ash4\u00252F351111\u00252F203\u00252F260478023976707_55781.mp4\u00253Foh\u00253D064626d4996116bdcde2d52f9b70e1f0\u002526oe\u00253D4E566C00\u002526l3s\u00253D20110823082632\u002526l3e\u00253D20110825083632\u002526lh\u00253D0dbcb2d22cd4dd5eb10bf
and then I expect this result :
http://video.l3.fbcdn.net/cfs-l3-ash4/351111...
But string is not replacing as expected
string[] BadCharacters = { "\\u00253A", "\\u00252F", "\\u00253F" };
string[] GoodCharacters = { ":", "/", "?" };
int i;
for (i = 0; i <= 2; i++)
{
textBox2.Text = textBox1.Text.Replace(BadCharacters[i], GoodCharacters[i]);
}

Your problem is your string gets stomped every iteration through the loop by going back to TextBox1.Text, you need to keep it in a local and keep using the changed value for the next substitution:
var changedText = textBox1.Text;
// always modify and assign to temp, that way we modify previous
for (i = 0; i <= 2; i++)
{
changedText = changedText.Replace(BadCharacters[i], GoodCharacters[i]);
}
textBox2.Text = changedText;

Try this:
var tmp = textBox1.Text;
for (i = 0; i <= 2; i++)
{
tmp = tmp.Replace(BadCharacters[i], GoodCharacters[i]);
}
textBox2.Text = tmp;

textBox2.Text will only ever contain one of the substitutions for each loop, so you likely see only the last iteration.
for (i = 0; i <= 2; i++)
{
textBox1.Text = textBox1.Text.Replace(BadCharacters[i], GoodCharacters[i]);
}
would likely provide the full substituted string desired.

You need to save the updated value of string each time you replace a substring. So save initial value of textBox1 to textBox2 and use it during iteration. In this way, you won't lose your updated string value.
textBox2.Text = textBox1.Text;
for(i = 0; i <= 2; i++)
{
textBox2.Text = textBox2.Text.Replace(BadCharacters[i], GoodCharacters[i]);
}
Also, by asssigning initial textBox1 value to textBox2 and using it inside your for loop, you save one assigmant statement.