task
Essentially, count the number of occurrences of =={{header| on each task page.

Output:

100 doors: 20 examples.
99 Bottles of Beer: 29 examples.
Abstract type: 10 examples.

Total: X examples.
For a full output, updated periodically, see Rosetta Code/Count examples/Full list.

You'll need to use the Media Wiki API, which you can find out about locally, here, or in Media Wiki's API documentation at, API:Query

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Net;
 
class Task {
    private string _task;
    private int _examples;
 
    public Task(string task, int examples) {
        _task = task;
        _examples = examples;
    }
 
    public string Name {
        get { return _task; }
    }
 
    public int Examples {
        get { return _examples; }
    }
 
    public override string ToString() {
        return String.Format("{0}: {1} examples.", this._task, this._examples);
    }
}
 
class Program {
    static List<string> GetTitlesFromCategory(string category, WebClient wc) {
        string content = wc.DownloadString(
            String.Format("http://www.rosettacode.org/w/api.php?action=query&list=categorymembers&cmtitle=Category:{0}&cmlimit=500&format=json", category)
        );
 
        return new Regex("\"title\":\"(.+?)\"").Matches(content).Cast<Match>().Select(x => x.Groups[1].Value.Replace("\\/", "/")).ToList();
    }
 
    static string GetSourceCodeFromPage(string page, WebClient wc) {
        return wc.DownloadString(
            String.Format("http://www.rosettacode.org/w/index.php?title={0}&action=raw", page)
        );
    }
 
    static void Main(string[] args) {
        WebClient wc = new WebClient();
        List<Task> tasks = new List<Task>();
        List<string> tasknames = GetTitlesFromCategory("Programming_Tasks", wc);
 
        foreach (string task in tasknames) {
            string content = GetSourceCodeFromPage(task, wc);
            int count = new Regex("=={{header", RegexOptions.IgnoreCase).Matches(content).Count;
            Task t = new Task(task, count);
 
            Console.WriteLine(t);
            tasks.Add(t);
        }
 
        Console.WriteLine("\nTotal: {0} examples.", tasks.Select(x => x.Examples).Sum());
    }
}