How does the foreach loop and if condition work?

Question

public static string returnLongestWord()
{
    string input = Console.ReadLine();
    string[] words = input.Split(' ');
    string maxWord = "";
    int ctr = 0;
    foreach (var word in words)
    {
        if (word.Length > ctr)
        {
            maxWord = word;
            ctr = word.Length;
        }
    }
    return maxWord;
}

My code basically locates the longest word in the users input.

The thing that is bugging me is the foreach loop. In general I imagine it goes through the array list of all the words.

Now the conditional loop if. I understand that if it is greater then 0 it is obviously a long word, but basically any word the user inputs is greater then 0, so how do these 2 loops determine the longest word ?

Answer 1

It's because a variable remembers the length of the word each iteration. If the word in an iteration is larger than the largest length seen in iterations before, this becomes the new length.

Its easy to see this happening when logging each iteration:

Online sample: https://dotnetfiddle.net/oFBicx

public class Program
{
    public static void Main()
    {
        var longestWord = returnLongestWord(new []{ "word1", "word12", "word1234", "mostdefinitelythelongestword!", "aShorterWord", "anotherShortWordThanTheMax"});

        Console.WriteLine("\nDone - longest word: " + longestWord);
    }

    public static string returnLongestWord(string[] words)
    {
        string maxWord = "";
        int ctr = 0;
        foreach (var word in words)
        {

            if (word.Length > ctr)
            {
                maxWord = word;
                ctr = word.Length;
            }

            Console.WriteLine("ctr: " + ctr + ", for word:\t " + maxWord);
        }
        return maxWord;
    }
}

outputs:

ctr: 5, for word:     word1
ctr: 6, for word:     word12
ctr: 8, for word:     word1234
ctr: 29, for word:     mostdefinitelythelongestword!
ctr: 29, for word:     mostdefinitelythelongestword!
ctr: 29, for word:     mostdefinitelythelongestword!

Done - longest word: mostdefinitelythelongestword!

This function can be writter a bit differently however, whilst still achieving the same, in a manner that is a bit easier to read. Right now both the maximum length of a string is kept in a variable ctr and the word for this length is remembered in maxWord. However, since we can calculate the length of the largest word we found, we don't need to remember this. In our condition we can then recalculate the length and use that to compare it to the current word instead:

online sample2: https://dotnetfiddle.net/4C7eZB

    public static void Main()
    {
        var longestWord = returnLongestWord(new []{ "word1", "word12", "word1234", "mostdefinitelythelongestword!", "aShorterWord", "anotherShortWordThanTheMax"});

        Console.WriteLine("\nDone - longest word: " + longestWord);
    }

    public static string returnLongestWord(string[] words)
    {
        string largestWordFound = string.Empty; 
        foreach (var word in words)
        {

            if (word.Length > largestWordFound.Length)
            {
                largestWordFound = word;
            }

            Console.WriteLine("Largest word length: " + largestWordFound.Length + ", for word:\t " + largestWordFound);
        }
        return largestWordFound;
    }

outputs:

Largest word length: 5, for word:     word1
Largest word length: 6, for word:     word12
Largest word length: 8, for word:     word1234
Largest word length: 29, for word:     mostdefinitelythelongestword!
Largest word length: 29, for word:     mostdefinitelythelongestword!
Largest word length: 29, for word:     mostdefinitelythelongestword!

Done - longest word: mostdefinitelythelongestword!

Answer 2

There is no if-loop or conditional loop. Only condition inside a loop. Those are perfectly normal. Usually you want to compare the values to something or do something with some of the values (processing)

This code seems to try to find the longest word. Doing so requires going through every word and comparing it to the previously longest word. This code stores the values for the previously longest word, using the variables maxWord and ctr. Both values are initialized for a Empty string, because the alterantive would be a ton of extra case handling in the if.

Note that you can do without ctr, and the name is actually somewhat problematic - sounding very similar to constructor. Just use maxWord.Lenght to compare it to the previous word lenght. But aside from that extra variable, that is also how I would do it.

foreach is a special variant of the for loop. It only goes forward, you got not indexer to manage and it can work with things like Enumerators. But the downside is that you can not change the collection while running over it. In this case the operation is purely reading, however - so no issues at all.

This is how I would change it:

public static string returnLongestWord()
{
    //Basic code to get some words from teh user
    //Could totally be left outside the function, just hand the array in as argument
    string input = Console.ReadLine();
    string[] words = input.Split(' ');

    //Let us start with a empty string as "longest Word"
    //That way I do not have to add a special case for the first word
    string maxWord = "";

    //Go over all strings in the collection of strings
    foreach (var currentWord in words)
    {
        //This string is beigger then the previous longest word. Guess it is the new longest word (thus far)
        if (currentWord.Length > maxWord.Lenght)
        {
            maxWord = currentWord ;
        }
    }
    //I am through all the words. So maxWord should now contain the longest word (or at least the first of them).
    return maxWord;
}