bool isLetter = !String.IsNullOrEmpty(segmentString) && Char.IsLetter(segmentString[0]);
if (isLetter == false)
{
do
{
segmentString = x12Reader.ReadNextSegment();
} while (!segmentString.StartsWith("ST") && !string.IsNullOrEmpty(segmentString));
}
Find String start with alphabets c#
Find String start with alphabets.