How to fill string with repeating it characters by text length?

Question

My text has 6 letters, my key has 4 letters. After XOR I get newText with only 4 letters. How can I make my key longer (repeat it till text length?

for ex.: string text = "flower",string key = "hell" I want to make my string key = "hellhe" and so on...)

private string XorText(string text,string key)
        {
            string newText = "";
            for (int i = 0; i < key.Length; i++)
            {
                int charValue = Convert.ToInt32(text[i]);
                int keyValue = Convert.ToInt32(key[i]);
                charValue ^= keyValue % 33;
                 newText += char.ConvertFromUtf32(charValue);
            }
            return newText;
        }

Instead of key[i] use key[i%key.Length] and change your for loop to use i < text.Length. Look up "modulus" to see how this works. — Matthew Watson
– Matthew Watson, Commented May 12, 2015 at 13:04

Mehrzad Chehraz · Accepted Answer · 2015-05-12 13:05:28Z

3

Use the remainder operator (%):

 private string XorText(string text,string key)
 {
      string newText = "";
      for (int i = 0; i < text.Length; i++)
      {
          int charValue = Convert.ToInt32(text[i]);
          int keyValue = Convert.ToInt32(key[i % key.Length]);
          charValue ^= keyValue % 33;
          newText += char.ConvertFromUtf32(charValue);
      }
      return newText;
  }

answered May 12, 2015 at 13:05

Mehrzad Chehraz

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Comments

General-Doomer · Accepted Answer · 2015-05-12 13:06:32Z

0

Use StringBuilder for string operations.

private string XorText(string text, string key)
{
    if (string.IsNullOrEmpty(text)) throw new ArgumentNullException("text");
    if (string.IsNullOrEmpty(key)) throw new ArgumentNullException("key");

    StringBuilder sb = new StringBuilder();

    int textLength = text.Length;
    int keyLength = key.Length;

    for (int i = 0; i < textLength; i++)
    {
        sb.Append((char)(text[i] ^ key[i % keyLength]));
    }

    return sb.ToString();
}

answered May 12, 2015 at 13:06

General-Doomer

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