How would I output part of a text document if I define a starting line and an ending line in C#?

I have a text document containing several different paragraphs of information. An excerpt of this file is included below, along with what I would like to use as the first and ending lines.

INCH TO FOOT (first line)
Divide inch measurement by 12.
END OF INCH TO FOOT (last line)

FOOT TO INCH (first line)
Multiply foot measurement by 12.
END OF FOOT TO INCH (last line)

An example of how I would like the output to appear if a user selects to view the inch to foot conversion formula.

Divide inch measurement by 12.

Any code suggestions would be appreciated. I am currently out of my league with this, and I have no idea where to start.

Thanks!

I have attempted to loop, but all I have managed is to output the full contents of the file.

As this looks like homework, I will first provide just the outline.

When you know you want the instructions for "FOOT TO INCH", assuming there may be multiple lines of instructions:

• Declare a boolean variable to mark when you are in the conversion paragraph you want. Set it to false initially.
• Read the file line-by-line
• Check whether the line is the conversion you want. If so, set that boolean variable to true.
• Else, when the line is "END OF " + your conversion, end the loop
• Else, when that boolean variable is true, print the line

How can the user select the specific conversion? You can print a list of available conversions and ask for one.

First get the list of conversions, assuming the first one starts at the first line and the rest after an empty line:

• Declare a boolean variable nextIsIdentifier and set to true
• Declare a list to fill: List<string> identifiers = new List<string>();
• Read the file, line-by-line
• When nextIsIdentifier is true, add this line to identifiers and set nextIsIdentifier to false
• Else, when the line is empty, set nextIsIdentifier to true

When the loop is done, that identifiers contains all conversions.

Now print that list, including an index number. You can ask the user for an index and then start searching the file for the instructions (see above).

Sample code

string source = @"INCH TO FOOT
Divide inch measurement by 12.
END OF INCH TO FOOT

FOOT TO INCH
Multiply foot measurement by 12.
END OF FOOT TO INCH

CELSIUS TO FAHRENHEIT
Multiply Celsius temperature by 9/5
Add 32
END OF CELSIUS TO FAHRENHEIT
";

// gather the headers
List<string> identifiers = new List<string>();
	
using (StringReader sr = new StringReader(source))
{
	bool nextIsIdentifier = true;
	string line;
	while ((line = sr.ReadLine()) != null)
	{
		if (nextIsIdentifier)
		{
			identifiers.Add(line);
			nextIsIdentifier = false;
		}
		else if (string.IsNullOrWhiteSpace(line))
		{
			nextIsIdentifier = true;
		}
	}
}

// print the headers, with an index
for (int i = 0; i < identifiers.Count; i++)
	Console.WriteLine($"{(i + 1)}. {identifiers[i]}");

// ask the user for an index
Console.Write($"enter number 1..{identifiers.Count}: ");
int index = int.Parse(Console.ReadLine());
// NB this will fail when the user inputs a non-integer or one outside the range
Console.WriteLine(index);

var identifier = identifiers[index-1];
Console.WriteLine($"Instructions for '{identifier}':");

// find the instructions
using (StringReader sr = new StringReader(source))
{
	string line;
	bool inParagraph = false;
	while ((line = sr.ReadLine()) != null)
	{
		if (line == identifier)
		{
            // next line is the start of the instructions
			inParagraph = true;
		}
		else if (line == "END OF " + identifier)
		{
            // done with the instructions
			break;
		}	
		else if (inParagraph)
		{
            // this is one line of instructions
			Console.WriteLine(line);
		}
	}
}

The easiest way is using regex:

string? TryParseInchToFoot(string text)
{
    var parser = new Regex(
@"INCH TO FOOT
(.*)
END OF INCH TO FOOT");

    var result = parser.Match(text);
    return result.Success
        ? result.Groups[1].Value
        : null;
}

And here is the usage example:

var sourcePath = "{YOUR_PATH_HERE}";
var source = File.ReadAllText(sourcePath);
var inchToFoot = TryParseInchToFoot(source);

I suggest it's study work with file format from a teacher, but anyway in real life it's much easier to use data-interchange formats like json. Here is the article - how to use json in .net

read line by line till you reach the first line, then output the next line

   var lines = File.ReadAllLines("file name");
   for(int i = 0; i < lines.Length; i++){
        if (lines[i] == "INCH TO FOOT")
             break;
    }
    if (i < lines.Length){
       var found = lines[i++];
       // here you have the line you want
    }

    using System;
    using System.IO;

    public class ConversionFormulaExtractor
    {
        public string GetConversionFormula(string conversionType)
        {
            string filePath = "path_to_your_text_document.txt"; // Replace with the actual file path
            string startLine = conversionType + " (first line)";
            string endLine = "END OF " + conversionType + " (last line)";

            string[] lines = File.ReadAllLines(filePath);
            int startIndex = -1;
            int endIndex = -1;

            for (int i = 0; i < lines.Length; i++)
            {
                if (lines[i].Contains(startLine))
                {
                    startIndex = i + 1;
                }
                else if (lines[i].Contains(endLine))
                {
                    endIndex = i;
                    break;
                }
            }

            if (startIndex != -1 && endIndex != -1)
            {
                string[] formulaLines = new string[endIndex - startIndex];
                Array.Copy(lines, startIndex, formulaLines, 0, endIndex - startIndex);
                string formula = string.Join(Environment.NewLine, formulaLines).Trim();
                return formula;
            }
            else
            {
                return "Conversion formula not found.";
            }
        }
    }

    class Program
    {
        static void Main()
        {
            string conversionType = "INCH TO FOOT";
            ConversionFormulaExtractor extractor = new ConversionFormulaExtractor();
            string conversionFormula = extractor.GetConversionFormula(conversionType);
            Console.WriteLine(conversionFormula);
        }
    }