C# - MultiConverter (DEZ-HEX-OKT-BIN)

int FromHex(string s) {
    int res = 0;
    foreach (char ch in s) {
      if ('0' <= ch && ch <= '9') res = 16 * res + (ch - '0');
      else if ('a' <= ch && ch <= 'f') res = 16 * res + (ch - 'a' + 10);
      else if ('A' <= ch && ch <= 'A') res = 16 * res + (ch - 'A' + 10);
      else throw new FormatException();
    }
    return res;
  }
  
  //----- convert decimal string to int
  int FromDec(string s) {
    int res = 0;
    foreach (char ch in s) {
      if ('0' <= ch && ch <= '9') res = 10 * res + (ch - '0');
      else throw new FormatException();
    }
    return res;
  }
  
  //----- convert octal string to int
  int FromOct(string s) {
    int res = 0;
    foreach (char ch in s) {
      if ('0' <= ch && ch <= '7') res = 8 * res + (ch - '0');
      else throw new FormatException();
    }
    return res;
  }
  
  //----- convert binary string to int
  int FromBin(string s) {
    int res = 0;
    foreach (char ch in s) {
      if (ch == '0') res = 2 * res;
      else if (ch == '1') res = 2 * res + 1;
      else throw new FormatException();
    }
    return res;
  }
  
  //----- parse and return the value of the TextBox val
  int Value() {
    string s = val.Text;
    if (s.Length == 0) throw new FormatException();
    else if (s.Length > 2 && s[0] == '0') {
      if (s[1] == 'x') return FromHex(s.Substring(2));
      else if (s[1] == 'o') return FromOct(s.Substring(2));
      else if (s[1] == 'b') return FromBin(s.Substring(2));
    }
    return FromDec(s);
  }
  
  //----- convert n to numeric string of base b
  string ToNumeric(int n, int b) {
    StringBuilder buf = new StringBuilder();
    do {
      buf.Append((char)(n % b + '0'));
      n = n / b;
    } while (n != 0);
    StringBuilder s = new StringBuilder();
    for (int i = buf.Length - 1; i >= 0; i--) s.Append(buf[i]);
    return s.ToString();
  }
  
  
  //-------------- event handlers ---------------------
  
  //---- Convert TextBox val to hexadecimal format
  public void ToHex(object sender, EventArgs e) {
    try {
      val.Text = "0x" + Value().ToString("x8");
      error.Text = "";
    } catch (FormatException) {
      error.Text = errMsg;
    }
  }
  
  //---- Convert TextBox val to decimal format
  public void ToDec(object sender, EventArgs e) {
    try {
      val.Text = Value().ToString();
      error.Text = "";
    } catch (FormatException) {
      error.Text = errMsg;
    }
  }
  
  //---- Convert TextBox val to octal format
  public void ToOct(object sender, EventArgs e) {
    try {
      val.Text = "0o" + ToNumeric(Value(), 8);
      error.Text = "";
    } catch (FormatException) {
      error.Text = errMsg;
    }
  }
  
  //---- Convert TextBox val to binary format
  public void ToBin(object sender, EventArgs e) {
    try {
      val.Text = "0b" + ToNumeric(Value(), 2);
      error.Text = "";
    } catch (FormatException) {
      error.Text = errMsg;
    }
  }
  
}
    
 }