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How to reverse an array of strings without changing the position of special characters in C#

I'm working on reversing a sentence. I'm able to do it. But I'm not sure, how to reverse the word without changing the special characters positions. I'm using regex but as soon as it finds the special characters it's stopping the reversal of the word.
Following is the code:
Console.WriteLine("Enter:");
string w = Console.ReadLine();
string rw = String.Empty;
String[] arr = w.Split(' ');
var regexItem = new Regex("^[a-zA-Z0-9]*$");
StringBuilder appendString = new StringBuilder();
for (int i = 0; i < arr.Length; i++)
{
char[] chararray = arr[i].ToCharArray();
for (int j = chararray.Length - 1; j >= 0; j--)
{
if (regexItem.IsMatch(rw))
{
rw = appendString.Append(chararray[j]).ToString();
}
}
sb.Append(' ');
}
Console.WriteLine(rw);
Console.ReadLine();
Example : Input
Marshall! Hello.
Expected output
llahsram! olleh.

A basic solution with regex and LINQ. Try it online.
public static void Main()
{
Console.WriteLine("Marshall! Hello.");
Console.WriteLine(Reverse("Marshall! Hello."));
}
public static string Reverse(string source)
{
// we split by groups to keep delimiters
var parts = Regex.Split(source, #"([^a-zA-Z0-9])");
// if we got a group of valid characters
var results = parts.Select(x => x.All(char.IsLetterOrDigit)
// we reverse it
? new string(x.Reverse().ToArray())
// or we keep the delimiters as it
: x);
// then we concat all of them
return string.Concat(results);
}
The same solution without LINQ. Try it online.
public static void Main()
{
Console.WriteLine("Marshall! Hello.");
Console.WriteLine(Reverse("Marshall! Hello."));
}
public static bool IsLettersOrDigits(string s)
{
foreach (var c in s)
{
if (!char.IsLetterOrDigit(c))
{
return false;
}
}
return true;
}
public static string Reverse(char[] s)
{
Array.Reverse(s);
return new string(s);
}
public static string Reverse(string source)
{
var parts = Regex.Split(source, #"([^a-zA-Z0-9])");
var results = new List<string>();
foreach(var x in parts)
{
results.Add(IsLettersOrDigits(x)
? Reverse(x.ToCharArray())
: x);
}
return string.Concat(results);
}

This is a solution without LINQ. I wasn't sure about what are considered special characters.
string sentence = "Marshall! Hello.";
List<string> words = sentence.Split(' ').ToList();
List<string> reversedWords = new List<string>();
foreach (string word in words)
{
char[] arr = new char[word.Length];
for( int i=0; i<word.Length; i++)
{
if(!Char.IsLetterOrDigit((word[i])))
{
for ( int x=0; x< i; x++)
{
arr[x] = arr[x + 1];
}
arr[i] = word[i];
}
else
{
arr[word.Length - 1 - i] = word[i];
}
}
reversedWords.Add(new string(arr));
}
string reversedSentence = string.Join(" ", reversedWords);
Console.WriteLine(reversedSentence);
And this is the output:
Updated Output = llahsraM! olleH.

Here is a non-regex version that does what you want:
var sentence = "Hello, john!";
var parts = sentence.Split(' ');
var reversed = new StringBuilder();
var charPositions = sentence.Select((c, idx) => new { Char = c, Index = idx })
.Where(_ => !char.IsLetterOrDigit(_.Char));
for (int i = 0; i < parts.Length; i++)
{
var chars = parts[i].ToCharArray();
for (int j = chars.Length - 1; j >= 0; j--)
{
if (char.IsLetterOrDigit(chars[j]))
{
reversed.Append(chars[j]);
}
}
}
foreach (var ch in charPositions)
{
reversed.Insert(ch.Index, ch.Char);
}
// olleH, nhoj!
Console.WriteLine(reversed.ToString());
Basically the trick is to remember the position of special (i.e. non letter or digit) characters and insert them at the end to those positions.

This solution is without LINQ and Regex. It may not be an efficient answer but working properly for small string values.
// This will reverse the string and special characters will just stay there.
public string ReverseString(string rString)
{
StringBuilder ss = new StringBuilder(rString);
int y = 0;
// The idea is to swap values. Like swapping first value with last one. It will keep swapping unless it reaches at the middle of the string where no swapping will be needed.
// This first loop is to detect first values.
for(int i=rString.Length-1;i>=0;i--)
{
// This condition is to check if the values is String or not. If it is not string then it is considered as special character which will just stay there at same old position.
if(Char.IsLetter(Convert.ToChar(rString.Substring(i,1))))
{
// This is second loop which is starting from end to swap values from end with first.
for (int k = y; k < rString.Length; k++)
{
// Again checking last values if values are string or not.
if (Char.IsLetter(Convert.ToChar(rString.Substring(k, 1))))
{
// This is swapping. So st1 is First value in that string
// st2 is the last item in that string
char st1 = Convert.ToChar(rString.Substring(k, 1));
char st2 = Convert.ToChar(rString.Substring(i, 1));
//This is swapping. So last item will go to first position and first item will go to last position, To make sure string is reversed.
// Remember when the string value is Special Character, swapping will move forward without swapping.
ss[rString.IndexOf(rString.Substring(i, 1))] = st1;
ss[rString.IndexOf(rString.Substring(k, 1))] = st2;
y++;
// When the swapping is done for first 2 items. The loop will stop to change the values.
break;
}
else
{
// This is just increment if value was Special character.
y++;
}
}
}
}
return ss.ToString();
}
Thanks!

Counting number of words in C#

I'm trying to count the number of words from a rich textbox in C# the code that I have below only works if it is a single line. How do I do this without relying on regex or any other special functions.
string whole_text = richTextBox1.Text;
string trimmed_text = whole_text.Trim();
string[] split_text = trimmed_text.Split(' ');
int space_count = 0;
string new_text = "";
foreach(string av in split_text)
{
if (av == "")
{
space_count++;
}
else
{
new_text = new_text + av + ",";
}
}
new_text = new_text.TrimEnd(',');
split_text = new_text.Split(',');
MessageBox.Show(split_text.Length.ToString ());

char[] delimiters = new char[] {' ', '\r', '\n' };
whole_text.Split(delimiters,StringSplitOptions.RemoveEmptyEntries).Length;

Since you are only interested in word count, and you don't care about individual words, String.Split could be avoided. String.Split is handy, but it unnecessarily generates a (potentially) large number of String objects, which in turn creates an unnecessary burden on the garbage collector. For each word in your text, a new String object needs to be instantiated, and then soon collected since you are not using it.
For a homework assignment, this may not matter, but if your text box contents change often and you do this calculation inside an event handler, it may be wiser to simply iterate through characters manually. If you really want to use String.Split, then go for a simpler version like Yonix recommended.
Otherwise, use an algorithm similar to this:
int wordCount = 0, index = 0;
// skip whitespace until first word
while (index < text.Length && char.IsWhiteSpace(text[index]))
index++;
while (index < text.Length)
{
// check if current char is part of a word
while (index < text.Length && !char.IsWhiteSpace(text[index]))
index++;
wordCount++;
// skip whitespace until next word
while (index < text.Length && char.IsWhiteSpace(text[index]))
index++;
}
This code should work better with cases where you have multiple spaces between each word, you can test the code online.

There are some better ways to do this, but in keeping with what you've got, try the following:
string whole_text = richTextBox1.Text;
string trimmed_text = whole_text.Trim();
// new line split here
string[] lines = trimmed_text.Split(Environment.NewLine.ToCharArray());
// don't need this here now...
//string[] split_text = trimmed_text.Split(' ');
int space_count = 0;
string new_text = "";
Now make two foreach loops. One for each line and one for counting words within the lines.
foreach (string line in lines)
{
// Modify the inner foreach to do the split on ' ' here
// instead of split_text
foreach (string av in line.Split(' '))
{
if (av == "")
{
space_count++;
}
else
{
new_text = new_text + av + ",";
}
}
}
new_text = new_text.TrimEnd(',');
// use lines here instead of split_text
lines = new_text.Split(',');
MessageBox.Show(lines.Length.ToString());
}

This was a phone screening interview question that I just took (by a large company located in CA who sells all kinds of devices that starts with a letter "i"), and I think I franked... after I got offline, I wrote this. I wish I were able to do it during interview..
static void Main(string[] args)
{
Debug.Assert(CountWords("Hello world") == 2);
Debug.Assert(CountWords(" Hello world") == 2);
Debug.Assert(CountWords("Hello world ") == 2);
Debug.Assert(CountWords("Hello world") == 2);
}
public static int CountWords(string test)
{
int count = 0;
bool wasInWord = false;
bool inWord = false;
for (int i = 0; i < test.Length; i++)
{
if (inWord)
{
wasInWord = true;
}
if (Char.IsWhiteSpace(test[i]))
{
if (wasInWord)
{
count++;
wasInWord = false;
}
inWord = false;
}
else
{
inWord = true;
}
}
// Check to see if we got out with seeing a word
if (wasInWord)
{
count++;
}
return count;
}

Have a look at the Lines property mentioned in #Jay Riggs comment, along with this overload of String.Split to make the code much simpler. Then the simplest approach would be to loop over each line in the Lines property, call String.Split on it, and add the length of the array it returns to a running count.
EDIT: Also, is there any reason you're using a RichTextBox instead of a TextBox with Multiline set to True?

I use an extension method for grabbing word count in a string. Do note, however, that double spaces will mess the count up.
public static int CountWords(this string line)
{
var wordCount = 0;
for (var i = 0; i < line.Length; i++)
if (line[i] == ' ' || i == line.Length - 1)
wordCount++;
return wordCount;
}
}

Your approach is on the right path. I would do something like, passing the text property of richTextBox1 into the method. This however won't be accurate if your rich textbox is formatting HTML, so you'll need to strip out any HTML tags prior to running the word count:
public static int CountWords(string s)
{
int c = 0;
for (int i = 1; i < s.Length; i++)
{
if (char.IsWhiteSpace(s[i - 1]) == true)
{
if (char.IsLetterOrDigit(s[i]) == true ||
char.IsPunctuation(s[i]))
{
c++;
}
}
}
if (s.Length > 2)
{
c++;
}
return c;
}

We used an adapted form of Yoshi's answer, where we fixed the bug where it would not count the last word in a string if there was no white-space after it:
public static int CountWords(string test)
{
int count = 0;
bool inWord = false;
foreach (char t in test)
{
if (char.IsWhiteSpace(t))
{
inWord = false;
}
else
{
if (!inWord) count++;
inWord = true;
}
}
return count;
}

using System.Collections;
using System;
class Program{
public static void Main(string[] args){
//Enter the value of n
int n = Convert.ToInt32(Console.ReadLine());
string[] s = new string[n];
ArrayList arr = new ArrayList();
//enter the elements
for(int i=0;i<n;i++){
s[i] = Console.ReadLine();
}
string str = "";
//Filter out duplicate values and store in arr
foreach(string i in s){
if(str.Contains(i)){
}else{
arr.Add(i);
}
str += i;
}
//Count the string with arr and s variables
foreach(string i in arr){
int count = 0;
foreach(string j in s){
if(i.Equals(j)){
count++;
}
}
Console.WriteLine(i+" - "+count);
}
}
}

int wordCount = 0;
bool previousLetterWasWhiteSpace = false;
foreach (char letter in keyword)
{
if (char.IsWhiteSpace(letter))
{
previousLetterWasWhiteSpace = true;
}
else
{
if (previousLetterWasWhiteSpace)
{
previousLetterWasWhiteSpace = false;
wordCount++;
}
}
}

public static int WordCount(string str)
{
int num=0;
bool wasInaWord=true;;
if (string.IsNullOrEmpty(str))
{
return num;
}
for (int i=0;i< str.Length;i++)
{
if (i!=0)
{
if (str[i]==' ' && str[i-1]!=' ')
{
num++;
wasInaWord=false;
}
}
if (str[i]!=' ')
{
wasInaWord=true;
}
}
if (wasInaWord)
{
num++;
}
return num;
}

class Program
{
static void Main(string[] args)
{
string str;
int i, wrd, l;
StringBuilder sb = new StringBuilder();
Console.Write("\n\nCount the total number of words in a string
:\n");
Console.Write("---------------------------------------------------
---\n");
Console.Write("Input the string : ");
str = Console.ReadLine();
l = 0;
wrd = 1;
foreach (var a in str)
{
sb.Append(a);
if (str[l] == ' ' || str[l] == '\n' || str[l] == '\t')
{
wrd++;
}
l++;
}
Console.WriteLine(sb.Replace(' ', '\n'));
Console.Write("Total number of words in the string is : {0}\n",
wrd);
Console.ReadLine();
}

This should work
input.Split(' ').ToList().Count;

This can show you the number of words in a line
string line = Console.ReadLine();
string[] word = line.Split(' ');
Console.WriteLine("Words " + word.Length);

You can also do it in this way!! Add this method to your extension methods.
public static int WordsCount(this string str)
{
return Regex.Matches(str, #"((\w+(\s?)))").Count;
}
And call it like this.
string someString = "Let me show how I do it!";
int wc = someString.WordsCount();

Iterating through string?

Not entirely sure this is possible, but say I have two strings like so:
"IAmAString-00001"
"IAmAString-00023"
What would be a quick'n'easy way to iterate from IAmAString-0001 to IAmAString-00023 by moving up the index of just the numbers on the end?
The problem is a bit more general than that, for example the string I could be dealing could be of any format but the last bunch of chars will always be numbers, so something like Super_Confusing-String#w00t0003 and in that case the last 0003 would be what I'd use to iterate through.
Any ideas?

You can use char.IsDigit:
static void Main(string[] args)
{
var s = "IAmAString-00001";
int index = -1;
for (int i = 0; i < s.Length; i++)
{
if (char.IsDigit(s[i]))
{
index = i;
break;
}
}
if (index == -1)
Console.WriteLine("digits not found");
else
Console.WriteLine("digits: {0}", s.Substring(index));
}
which produces this output:
digits: 00001

string.Format and a for loop should do what you want.
for(int i = 0; i <=23; i++)
{
string.Format("IAmAString-{0:D4}",i);
}
or something close to that (not sitting in front of a compiler).

string start = "IAmAString-00001";
string end = "IAmAString-00023";
// match constant part and ending digits
var matchstart = Regex.Match(start,#"^(.*?)(\d+)$");
int numberstart = int.Parse(matchstart.Groups[2].Value);
var matchend = Regex.Match(end,#"^(.*?)(\d+)$");
int numberend = int.Parse(matchend.Groups[2].Value);
// constant parts must be the same
if (matchstart.Groups[1].Value != matchend.Groups[1].Value)
throw new ArgumentException("");
// create a format string with same number of digits as original
string format = new string('0', matchstart.Groups[2].Length);
for (int ii = numberstart; ii <= numberend; ++ii)
Console.WriteLine(matchstart.Groups[1].Value + ii.ToString(format));

You could use a Regex:
var match=Regex.Match("Super_Confusing-String#w00t0003",#"(?<=(^.*\D)|^)\d+$");
if(match.Success)
{
var val=int.Parse(match.Value);
Console.WriteLine(val);
}
To answer more specifically, you could use named groups to extract what you need:
var match=Regex.Match(
"Super_Confusing-String#w00t0003",
#"(?<prefix>(^.*\D)|^)(?<digits>\d+)$");
if(match.Success)
{
var prefix=match.Groups["prefix"].Value;
Console.WriteLine(prefix);
var val=int.Parse(match.Groups["digits"].Value);
Console.WriteLine(val);
}

If you can assume that the last 5 characters are the number then:
string prefix = "myprefix-";
for (int i=1; i <=23; i++)
{
Console.WriteLine(myPrefix+i.ToString("D5"));
}

This function will find the trailing number.
private int FindTrailingNumber(string str)
{
string numString = "";
int numTest;
for (int i = str.Length - 1; i > 0; i--)
{
char c = str[i];
if (int.TryParse(c.ToString(), out numTest))
{
numString = c + numString;
}
}
return int.Parse(numString);
}
Assuming all your base strings are the same, this would iterate between strings.
string s1 = "asdf123";
string s2 = "asdf127";
int num1 = FindTrailingNumber(s1);
int num2 = FindTrailingNumber(s2);
string strBase = s1.Replace(num1.ToString(), "");
for (int i = num1; i <= num2; i++)
{
Console.WriteLine(strBase + i.ToString());
}

I think it would be better if you do the search from the last (Rick already upvoted you since it was ur logic :-))
static void Main(string[] args)
{
var s = "IAmAString-00001";
int index = -1;
for (int i = s.Length - 1; i >=0; i--)
{
if (!char.IsDigit(s[i]))
{
index = i;
break;
}
}
if (index == -1)
Console.WriteLine("digits not found");
else
Console.WriteLine("digits: {0}", s.Substring(index));
Console.ReadKey();
}
HTH

If the last X numbers are always digits, then:
int x = 5;
string s = "IAmAString-00001";
int num = int.Parse(s.Substring(s.Length - x, x));
Console.WriteLine("Your Number is: {0}", num);
If the last digits can be 3, 4, or 5 in length, then you will need a little more logic:
int x = 0;
string s = "IAmAString-00001";
foreach (char c in s.Reverse())//Use Reverse() so you start with digits only.
{
if(char.IsDigit(c) == false)
break;//If we start hitting non-digit characters, then exit the loop.
++x;
}
int num = int.Parse(s.Substring(s.Length - x, x));
Console.WriteLine("Your Number is: {0}", num);
I'm not good with complicated RegEx. Because of this, I always shy away from it when maximum optimization is unnecessary. The reason for this is RegEx doesn't always parse strings the way you expect it to. If there is and alternate solution that will still run fast then I'd rather go that route as it's easier for me to understand and know that it will work with any combination of strings.
For Example: if you use some of the other solutions presented here with a string like "I2AmAString-000001", then you will get "2000001" as your number instead of "1".

split a string with max character limit

I'm attempting to split a string into many strings (List) with each one having a maximum limit of characters. So say if I had a string of 500 characters, and I want each string to have a max of 75, there would be 7 strings, and the last one would not have a full 75.
I've tried some of the examples I have found on stackoverflow, but they 'truncate' the results. Any ideas?

You can write your own extension method to do something like that
static class StringExtensions
{
public static IEnumerable<string> SplitOnLength(this string input, int length)
{
int index = 0;
while (index < input.Length)
{
if (index + length < input.Length)
yield return input.Substring(index, length);
else
yield return input.Substring(index);
index += length;
}
}
}
And then you could call it like this
string temp = new string('#', 500);
string[] array = temp.SplitOnLength(75).ToArray();
foreach (string x in array)
Console.WriteLine(x);

I think this is a little cleaner than the other answers:
public static IEnumerable<string> SplitByLength(string s, int length)
{
while (s.Length > length)
{
yield return s.Substring(0, length);
s = s.Substring(length);
}
if (s.Length > 0) yield return s;
}

I would tackle this with a loop using C# String.Substring method.
Note that this isn't exact code, but you get the idea.
var myString = "hello world";
List<string> list = new List();
int maxSize
while(index < myString.Length())
{
if(index + maxSize > myString.Length())
{
// handle last case
list.Add(myString.Substring(index));
break;
}
else
{
list.Add(myString.Substring(index,maxSize));
index+= maxSize;
}
}

When you say split, are you referring to the split function? If not, something like this will work:
List<string> list = new List<string>();
string s = "";
int num = 75;
while (s.Length > 0)
{
list.Add(s.Substring(0, num));
s = s.Remove(0, num);
}

i am assuming maybe a delimiter - like space character.
search on the string (instr) until you find the next position of the delimiter.
if that is < your substring length (75) then append to the current substring.
if not, start a new substring.
special case - if there is no delimiter in the entire substring - then you need to define what happens - like add a '-' then continue.

public static string SplitByLength(string s, int length)
{
ArrayList sArrReturn = new ArrayList();
String[] sArr = s.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
foreach (string sconcat in sArr)
{
if (((String.Join(" ", sArrReturn.ToArray()).Length + sconcat.Length)+1) < length)
sArrReturn.Add(sconcat);
else
break;
}
return String.Join(" ", sArrReturn.ToArray());
}
public static string SplitByLengthOld(string s, int length)
{
try
{
string sret = string.Empty;
String[] sArr = s.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
foreach (string sconcat in sArr)
{
if ((sret.Length + sconcat.Length + 1) < length)
sret = string.Format("{0}{1}{2}", sret, string.IsNullOrEmpty(sret) ? string.Empty : " ", sconcat);
}
return sret;
}
catch
{
return string.Empty;
}
}

Finding multiple indexes from source string

Basically I need to do String.IndexOf() and I need to get array of indexes from the source string.
Is there easy way to get array of indexes?
Before asking this question I have Googled a lot, but have not found easy solution to solve this simple problem.

How about this extension method:
public static IEnumerable<int> IndexesOf(this string haystack, string needle)
{
int lastIndex = 0;
while (true)
{
int index = haystack.IndexOf(needle, lastIndex);
if (index == -1)
{
yield break;
}
yield return index;
lastIndex = index + needle.Length;
}
}
Note that when looking for "AA" in "XAAAY" this code will now only yield 1.
If you really need an array, call ToArray() on the result. (This is assuming .NET 3.5 and hence LINQ support.)

var indexs = "Prashant".MultipleIndex('a');
//Extension Method's Class
public static class Extensions
{
static int i = 0;
public static int[] MultipleIndex(this string StringValue, char chChar)
{
var indexs = from rgChar in StringValue
where rgChar == chChar && i != StringValue.IndexOf(rgChar, i + 1)
select new { Index = StringValue.IndexOf(rgChar, i + 1), Increament = (i = i + StringValue.IndexOf(rgChar)) };
i = 0;
return indexs.Select(p => p.Index).ToArray<int>();
}
}

You would have to loop, I suspect:
int start = 0;
string s = "abcdeafghaji";
int index;
while ((index = s.IndexOf('a', start)) >= 0)
{
Console.WriteLine(index);
start = index + 1;
}

Using a solution that utilizes regex can be more reliable, using the indexOf function can be unreliable. It will find all matches and indexes, not matching an exact phrase which can lead to unexpected results. This function resolves that by making use of the Regex library.
public static IEnumerable<int> IndexesOf(string haystack, string needle)
{
Regex r = new Regex("\\b(" + needle + ")\\b");
MatchCollection m = r.Matches(haystack);
return from Match o in m select o.Index;
}