How to do String formatting
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private void Submit_Click(object sender, EventArgs e) {

try
{

string valueToConvert = Value.Text;

switch (FormatType.SelectedItem.Value)
{

// Number formats
case "Currency":
FormattedValue.Text = decimal.Parse(valueToConvert).ToString( "C5" );
//you can add a number to the end to specify precision
FormatExpression.Text = "decimal.Parse(valueToConvert).ToString( \"C5\"
)";
break;
case "Decimal":
FormattedValue.Text = decimal.Parse(valueToConvert).ToString( "D5" );
//you can add a number to the end to specify precision
FormatExpression.Text = "decimal.Parse(valueToConvert).ToString( \"D5\"
)";
break;
case "Scientific":
FormattedValue.Text = decimal.Parse(valueToConvert).ToString( "E" );
FormatExpression.Text = "decimal.Parse(valueToConvert).ToString( \"E\"
)";
break;
case "Fixed-point":
FormattedValue.Text = decimal.Parse(valueToConvert).ToString( "F5" );
//you can add a number to the end to specify precision
FormatExpression.Text = "decimal.Parse(valueToConvert).ToString( \"F5\"
)";
break;
case "General":
FormattedValue.Text = decimal.Parse(valueToConvert).ToString( "G" );
FormatExpression.Text = "decimal.Parse(valueToConvert).ToString( \"G\"
)";
break;
case "Number":
FormattedValue.Text = decimal.Parse(valueToConvert).ToString( "N" );
FormatExpression.Text = "decimal.Parse(valueToConvert).ToString( \"N\"
)";
break;
case "Percent":
FormattedValue.Text = decimal.Parse(valueToConvert).ToString( "P" );
FormatExpression.Text = "decimal.Parse(valueToConvert).ToString( \"P\"
)";
break;
case "Round-trip":
FormattedValue.Text = decimal.Parse(valueToConvert).ToString( "R" );
FormatExpression.Text = "decimal.Parse(valueToConvert).ToString( \"R\"
)";
break;
case "Hexadecimal":
FormattedValue.Text = decimal.Parse(valueToConvert).ToString( "X" );
FormatExpression.Text = "decimal.Parse(valueToConvert).ToString( \"X\"
)";
break;

// Date Formats
case "Short Date Pattern":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "d" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"d\"
)";
break;
case "Long Date Pattern":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "D" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"D\"
)";
break;
case "Short Time Pattern":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "t" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"t\"
)";
break;
case "Long Time Pattern":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "T" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"T\"
)";
break;
case "Full Date/Time Pattern (short time)":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "f" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"f\"
)";
break;
case "Full Date/Time Pattern (long time)":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "F" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"F\"
)";
break;
case "General Date/Time Pattern (short time)":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "g" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"g\"
)";
break;
case "General Date/Time Pattern (long time)":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "G" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"G\"
)";
break;
case "Month Day Pattern":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "M" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"M\"
)";
break;
case "RFC1123 Pattern":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "R" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"R\"
)";
break;
case "Sortable Date/Time Pattern; conforms to ISO 8601":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "s" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"s\"
)";
break;
case "Universal Sortable Date/Time Pattern":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "u" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"u\"
)";
break;
case "Universal Full Sortable Date/Time Pattern":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "U" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"U\"
)";
break;
case "Year Month Pattern":
FormattedValue.Text = DateTime.Parse(valueToConvert).ToString( "Y" );
FormatExpression.Text = "DateTime.Parse(valueToConvert).ToString( \"Y\"
)";
break;
case "Custom Date Time":
FormattedValue.Text = DateTime.Now.ToString( "yyyy/mm/dd" );
FormatExpression.Text = "DateTime.Now.ToString( \"yyyy/mm/dd\" )";
break;

default:
FormattedValue.Text = Value.Text;
break;



}

}
catch (Exception Ex) {

FormattedValue.Text = ""+Ex.Message+"";
FormatExpression.Text = String.Empty;

}

}