Task: Text between
C#: using System;

namespace TextBetween {
    class Program {
        static string TextBetween(string source, string beg, string end) {
            int startIndex;

            if (beg == "start") {
                startIndex = 0;
            }
            else {
                startIndex = source.IndexOf(beg);
                if (startIndex < 0) {
                    return "";
                }
                startIndex += beg.Length;
            }

            int endIndex = source.IndexOf(end, startIndex);
            if (endIndex < 0 || end == "end") {
                return source.Substring(startIndex);
            }
            return source.Substring(startIndex, endIndex - startIndex);
        }

        static void Print(string s, string b, string e) {
            Console.WriteLine("text: '{0}'", s);
            Console.WriteLine("start: '{0}'", b);
            Console.WriteLine("end: '{0}'", e);
            Console.WriteLine("result: '{0}'", TextBetween(s, b, e));
            Console.WriteLine();
        }

        static void Main(string[] args) {
            Print("Hello Rosetta Code world", "Hello ", " world");
            Print("Hello Rosetta Code world", "start", " world");
            Print("Hello Rosetta Code world", "Hello ", "end");
            Print("</div><div style=\"chinese\">你好嗎</div>", "<div style=\"chinese\">", "</div>");
            Print("<text>Hello <span>Rosetta Code</span> world</text><table style=\"myTable\">", "<text>", "<table>");
            Print("<table style=\"myTable\"><tr><td>hello world</td></tr></table>", "<table>", "</table>");
            Print("The quick brown fox jumps over the lazy other fox", "quick ", " fox");
            Print("One fish two fish red fish blue fish", "fish ", " red");
            Print("FooBarBazFooBuxQuux", "Foo", "Foo");
        }
    }
}

Go: package main

import (
    "fmt"
    "strings"
)

func textBetween(str, start, end string) string {
    if str == "" || start == "" || end == "" {
        return str
    }
    s := 0
    if start != "start" {
        s = strings.Index(str, start)
    }
    if s == -1 {
        return ""
    }
    si := 0
    if start != "start" {
        si = s + len(start)
    }
    e := len(str)
    if end != "end" {
        e = strings.Index(str[si:], end)
        if e == -1 {
            return str[si:]
        }
        e += si
    }
    return str[si:e]
}

func main() {
    texts := [9]string{
        "Hello Rosetta Code world",
        "Hello Rosetta Code world",
        "Hello Rosetta Code world",
        "</div><div style=\"chinese\">你好嗎</div>",
        "<text>Hello <span>Rosetta Code</span> world</text><table style=\"myTable\">",
        "<table style=\"myTable\"><tr><td>hello world</td></tr></table>",
        "The quick brown fox jumps over the lazy other fox",
        "One fish two fish red fish blue fish",
        "FooBarBazFooBuxQuux",
    }
    starts:= [9]string{
        "Hello ", "start", "Hello ", "<div style=\"chinese\">",
        "<text>", "<table>", "quick ", "fish ", "Foo",
    }
    ends := [9]string{
        " world", " world", "end", "</div>", "<table>",
        "</table>", " fox", " red", "Foo",
    }
    for i, text := range texts {
        fmt.Printf("Text: \"%s\"\n", text)
        fmt.Printf("Start delimiter: \"%s\"\n", starts[i])
        fmt.Printf("End delimiter: \"%s\"\n", ends[i])
        b := textBetween(text, starts[i], ends[i])
        fmt.Printf("Output: \"%s\"\n\n", b)
    }
}